diff --git a/cli.mjs b/cli.mjs
index 82f8c900..a60227a2 100644
--- a/cli.mjs
+++ b/cli.mjs
@@ -1,8 +1,9 @@
 import { checkbox, confirm, expand, input, select } from "@inquirer/prompts";
 import fsExtra from "fs-extra";
 
-import { cert, initializeApp } from "firebase-admin/app"; // eslint-disable-line import/no-unresolved
-import { getFirestore } from "firebase-admin/firestore"; // eslint-disable-line import/no-unresolved
+import { cert, initializeApp } from "firebase-admin/app";
+import { getFirestore } from "firebase-admin/firestore";
+import { Command } from "commander";
 
 /** -------------------- GLOBALS -------------------- */
 
@@ -17,16 +18,86 @@ let OUTPUT_ROOT; // The root in which data is saved
 const INVALID_ACTION_ERROR = new Error("Invalid action: " + ACTION);
 const INVALID_DEPLOYMENT_ERROR = new Error("Invalid deployment: " + DEPLOYMENT);
 
+/** -------------------- COMMANDER -------------------- */
+const commander = new Command();
+// default: [download | delete | register ] not provided, run main() as usual continuing with prompting
+commander.action(() => {});
+
+// download: optional argument studyID and participantID skips relative prompts
+commander
+  .command(`download`)
+  .argument(`[studyID]`)
+  .argument(`[participantID]`)
+  .description(`Download experiment data from Firebase provided study ID and participant ID`)
+  .action((studyID, participantID) => {
+    ACTION = "download";
+    STUDY_ID = studyID;
+    PARTICIPANT_ID = participantID;
+  });
+
+// delete: optional argument studyID and participantID skips relative prompts
+commander
+  .command(`delete`)
+  .argument(`[studyID]`)
+  .argument(`[participantID]`)
+  .description(`Delete experiment data from Firebase provided study ID and participant ID`)
+  .action((studyID, participantID) => {
+    ACTION = "delete";
+    STUDY_ID = studyID;
+    PARTICIPANT_ID = participantID;
+  });
+
+// register: optional argument studyID and participantID skips relative prompts
+commander
+  .command(`register`)
+  .argument(`[studyID]`)
+  .argument(`[participantID]`)
+  .description(
+    `Register new partipant under study provided a partipantID and studyID; new study will be created if not found`
+  )
+  .action((studyID, participantID) => {
+    ACTION = "register";
+    STUDY_ID = studyID;
+    PARTICIPANT_ID = participantID;
+  });
+
 /** -------------------- MAIN -------------------- */
 
-// TODO @brown-ccv #289: Pass CLI arguments with commander (especially for action)
 async function main() {
-  ACTION = await actionPrompt();
+  commander.parse();
+  // print message if download or delete provided, along with optional args provided
+  if (ACTION != undefined) {
+    console.log(
+      `${ACTION} data from Firebase ${STUDY_ID === undefined ? "" : `given study ID: ${STUDY_ID}`} ${PARTICIPANT_ID === undefined ? "" : `and participant ID: ${PARTICIPANT_ID}`}`
+    );
+  }
+
+  if (ACTION === undefined) {
+    ACTION = await actionPrompt();
+  }
   DEPLOYMENT = await deploymentPrompt();
   // TODO @brown-ccv #291: Enable downloading all study data at once
-  STUDY_ID = await studyIDPrompt();
+  if (STUDY_ID === undefined) {
+    STUDY_ID = await studyIDPrompt();
+  } else {
+    // when args directly passed in through CLI, check if study is valid
+    const studyCollection = await validateStudyFirebase(STUDY_ID);
+    if (!studyCollection && ACTION !== "register") {
+      console.error("Please enter a valid study from your Firestore database");
+      process.exit(1);
+    }
+  }
   // TODO @brown-ccv #291: Enable downloading all participant data at once
-  PARTICIPANT_ID = await participantIDPrompt();
+  if (PARTICIPANT_ID === undefined) {
+    PARTICIPANT_ID = await participantIDPrompt();
+  } else {
+    // when args directly passed in through CLI, check if participant is valid
+    const participantCollection = await validateParticipantFirebase(PARTICIPANT_ID);
+    if (!participantCollection && ACTION !== "register") {
+      console.error(`Please enter a valid participant on the study "${STUDY_ID}"`);
+      process.exit(1);
+    }
+  }
   EXPERIMENT_IDS = await experimentIDPrompt();
 
   switch (ACTION) {
@@ -49,6 +120,15 @@ async function main() {
           throw INVALID_DEPLOYMENT_ERROR;
       }
       break;
+    case "register":
+      switch (DEPLOYMENT) {
+        case "firebase":
+          await registerDataFirebase(STUDY_ID, PARTICIPANT_ID);
+          break;
+        default:
+          throw INVALID_DEPLOYMENT_ERROR;
+      }
+      break;
     default:
       throw INVALID_ACTION_ERROR;
   }
@@ -140,6 +220,24 @@ async function deleteDataFirebase() {
   } else console.log("Skipping deletion");
 }
 
+/** -------------------- REGISTER ACTION -------------------- */
+
+/** Register new data, write to Firestore */
+async function registerDataFirebase(studyID, participantID) {
+  const confirmation = await confirmRegisterPrompt(studyID, participantID);
+  if (confirmation) {
+    try {
+      await addStudyAndParticipant(studyID, participantID);
+    } catch (error) {
+      console.error(
+        `Unable to register new participant with participantID ${participantID} under studyID ${studyID}: ` +
+          error
+      );
+    }
+  } else console.log("Skipping registration");
+  return true;
+}
+
 /** -------------------- PROMPTS -------------------- */
 
 /** Prompt the user for the action they are trying to complete */
@@ -151,6 +249,10 @@ async function actionPrompt() {
         name: "Download data",
         value: "download",
       },
+      {
+        name: "Register new participant under study",
+        value: "register",
+      },
       {
         name: "Delete data",
         value: "delete",
@@ -183,23 +285,20 @@ async function deploymentPrompt() {
   return response;
 }
 
-/** Prompt the user to enter the ID of a study */
 async function studyIDPrompt() {
   const invalidMessage = "Please enter a valid study from your Firestore database";
-  const validateStudyFirebase = async (input) => {
-    // subcollection is programmatically generated, if it doesn't exist then input must not be a valid studyID
-    const studyIDCollections = await getStudyRef(input).listCollections();
-    return studyIDCollections.find((c) => c.id === PARTICIPANTS_COL) ? true : invalidMessage;
-  };
-
   return await input({
     message: "Select a study:",
     validate: async (input) => {
       if (!input) return invalidMessage;
-
+      if (ACTION === "register") {
+        STUDY_ID = input;
+        return true;
+      }
       switch (DEPLOYMENT) {
         case "firebase":
-          return validateStudyFirebase(input);
+          const studyCollection = await validateStudyFirebase(input);
+          return !studyCollection ? invalidMessage : true;
         default:
           throw INVALID_DEPLOYMENT_ERROR;
       }
@@ -207,25 +306,22 @@ async function studyIDPrompt() {
   });
 }
 
-/** Prompt the user to enter the ID of a participant on the STUDY_ID study */
 async function participantIDPrompt() {
   const invalidMessage = `Please enter a valid participant on the study "${STUDY_ID}"`;
-  const validateParticipantFirebase = async (input) => {
-    // subcollection is programmatically generated, if it doesn't exist then input must not be a valid participantID
-    const studyIDCollections = await getParticipantRef(STUDY_ID, input).listCollections();
-    return studyIDCollections.find((c) => c.id === DATA_COL) ? true : invalidMessage;
-  };
-
   return await input({
-    message: "Select a participant:",
+    message: ACTION === "register" ? "Enter a new participant:" : "Select a participant:",
     validate: async (input) => {
       const invalid = "Please enter a valid participant from your Firestore database";
       if (!input) return invalid;
       else if (input === "*") return true;
-
+      if (ACTION === "register") {
+        PARTICIPANT_ID = input;
+        return true;
+      }
       switch (DEPLOYMENT) {
         case "firebase":
-          return validateParticipantFirebase(input);
+          const participantCollection = await validateParticipantFirebase(input);
+          return !participantCollection ? invalidMessage : true;
         default:
           throw INVALID_DEPLOYMENT_ERROR;
       }
@@ -235,6 +331,11 @@ async function participantIDPrompt() {
 
 /** Prompt the user to select one or more experiments of the PARTICIPANT_ID on STUDY_ID */
 async function experimentIDPrompt() {
+  // register: adding/checking for existing new studies will be done in function
+  if (ACTION === "register") {
+    return;
+  }
+
   const dataSnapshot = await getDataRef(STUDY_ID, PARTICIPANT_ID).get();
 
   // Sort experiment choices by most recent first
@@ -278,6 +379,20 @@ async function confirmDeletionPrompt() {
   });
 }
 
+async function confirmRegisterPrompt(studyID, participantID) {
+  const currentParticipants = await getRegisteredParticipantArr(studyID);
+  const currentParticipantMessage =
+    currentParticipants.length === 0
+      ? "Currently, there are no participants under this study\n"
+      : `Currently, the participants under this study include: \n${currentParticipants.join("\n")}\n`;
+  return confirm({
+    message:
+      currentParticipantMessage +
+      `Continue? adding study with studyID: ${studyID} and participant ID: ${participantID}`,
+    default: false,
+  });
+}
+
 /**
  * Prompts the user to confirm continuation of the CLI, including future conflicts
  * @param {string} outputFile
@@ -312,9 +427,25 @@ async function confirmOverwritePrompt(file, overwriteAll) {
   return answer;
 }
 
+/** -------------------- FIRESTORE VALIDATIONS -------------------- */
+/** helper to check if the given study (input) is in firestore */
+async function validateStudyFirebase(input) {
+  // subcollection is programmatically generated, if it doesn't exist then input must not be a valid studyID
+  const studyIDCollections = await getStudyRef(input).listCollections();
+  return studyIDCollections.find((c) => c.id === PARTICIPANTS_COL);
+}
+
+/** helper to check if the given participant (input) is in firestore under study */
+async function validateParticipantFirebase(input) {
+  // subcollection is programmatically generated, if it doesn't exist then input must not be a valid participantID
+  const studyIDCollections = await getParticipantRef(STUDY_ID, input).listCollections();
+  return studyIDCollections.find((c) => c.id === DATA_COL);
+}
+
 /** -------------------- FIRESTORE HELPERS -------------------- */
 
 const RESPONSES_COL = "participant_responses";
+const REG_STUDY_COL = "registered_studies";
 const PARTICIPANTS_COL = "participants";
 const DATA_COL = "data";
 const TRIALS_COL = "trials";
@@ -333,3 +464,42 @@ const getDataRef = (studyID, participantID) =>
 // Get a reference to a participant's specific experiment data document in Firestore
 const getExperimentRef = (studyID, participantID, experimentID) =>
   getDataRef(studyID, participantID).doc(experimentID);
+
+// Get a reference to a registered study
+const getRegisteredfStudyRef = (studyID) => FIRESTORE.collection(REG_STUDY_COL).doc(studyID);
+
+// Get current registered participant array under the StudyID
+const getRegisteredParticipantArr = async (studyID) => {
+  const data = await getRegisteredfStudyRef(studyID).get();
+  if (data["_fieldsProto"] !== undefined) {
+    // get array of registered participant under study
+    return data["_fieldsProto"]["registered_participants"]["arrayValue"]["values"]
+      .filter((item) => item.valueType === "stringValue")
+      .map((item) => item.stringValue);
+  } else {
+    // return empty array when no participant found
+    return [];
+  }
+};
+
+// Register new participantID under the provided studyID
+const registerNewParticipant = async (studyID, participantID) => {
+  const currParticipants = await getRegisteredParticipantArr(studyID);
+  const newParticipantArray = [...currParticipants, participantID];
+  const newData = { registered_participants: newParticipantArray };
+  getRegisteredfStudyRef(studyID).update(newData);
+  console.log(
+    `Successfully added study and participant. Current participantIDs under study ${studyID}: \n${newParticipantArray.join("\n")}`
+  );
+};
+
+// Add new participantID under studyID to Firestore under registered_studies,
+//  creates new study if studyID doesn't exist
+const addStudyAndParticipant = async (studyID, participantID) => {
+  const data = await getRegisteredfStudyRef(studyID).get();
+  if (data["_fieldsProto"] === undefined) {
+    // study not initiated yet
+    await getRegisteredfStudyRef(studyID).set({ registered_participants: [] });
+  }
+  await registerNewParticipant(studyID, participantID);
+};
diff --git a/package-lock.json b/package-lock.json
index 1981eae6..47f00e60 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -22,6 +22,7 @@
         "@jspsych/plugin-instructions": "^1.1.3",
         "@jspsych/plugin-preload": "^1.1.2",
         "@jspsych/plugin-survey": "^1.0.1",
+        "commander": "^12.1.0",
         "electron-log": "^5.0.0",
         "electron-squirrel-startup": "^1.0.0",
         "firebase": "^10.11.0",
@@ -655,6 +656,15 @@
         "node": ">= 16.4.0"
       }
     },
+    "node_modules/@electron-forge/cli/node_modules/commander": {
+      "version": "4.1.1",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-4.1.1.tgz",
+      "integrity": "sha512-NOKm8xhkzAjzFx8B2v5OAHT+u5pRQc2UCa2Vq9jYL/31o2wi9mxBA7LIFs3sV5VSC49z6pEhfbMULvShKj26WA==",
+      "dev": true,
+      "engines": {
+        "node": ">= 6"
+      }
+    },
     "node_modules/@electron-forge/cli/node_modules/fs-extra": {
       "version": "10.1.0",
       "resolved": "https://registry.npmjs.org/fs-extra/-/fs-extra-10.1.0.tgz",
@@ -6306,13 +6316,11 @@
       }
     },
     "node_modules/commander": {
-      "version": "4.1.1",
-      "resolved": "https://registry.npmjs.org/commander/-/commander-4.1.1.tgz",
-      "integrity": "sha512-NOKm8xhkzAjzFx8B2v5OAHT+u5pRQc2UCa2Vq9jYL/31o2wi9mxBA7LIFs3sV5VSC49z6pEhfbMULvShKj26WA==",
-      "dev": true,
-      "license": "MIT",
+      "version": "12.1.0",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-12.1.0.tgz",
+      "integrity": "sha512-Vw8qHK3bZM9y/P10u3Vib8o/DdkvA2OtPtZvD871QKjy74Wj1WSKFILMPRPSdUSx5RFK1arlJzEtA4PkFgnbuA==",
       "engines": {
-        "node": ">= 6"
+        "node": ">=18"
       }
     },
     "node_modules/commitizen": {
@@ -9638,6 +9646,15 @@
         "node": ">= 10"
       }
     },
+    "node_modules/firebase-tools/node_modules/commander": {
+      "version": "4.1.1",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-4.1.1.tgz",
+      "integrity": "sha512-NOKm8xhkzAjzFx8B2v5OAHT+u5pRQc2UCa2Vq9jYL/31o2wi9mxBA7LIFs3sV5VSC49z6pEhfbMULvShKj26WA==",
+      "dev": true,
+      "engines": {
+        "node": ">= 6"
+      }
+    },
     "node_modules/firebase-tools/node_modules/fs-extra": {
       "version": "10.1.0",
       "resolved": "https://registry.npmjs.org/fs-extra/-/fs-extra-10.1.0.tgz",
@@ -12539,16 +12556,6 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
-    "node_modules/lint-staged/node_modules/commander": {
-      "version": "12.1.0",
-      "resolved": "https://registry.npmjs.org/commander/-/commander-12.1.0.tgz",
-      "integrity": "sha512-Vw8qHK3bZM9y/P10u3Vib8o/DdkvA2OtPtZvD871QKjy74Wj1WSKFILMPRPSdUSx5RFK1arlJzEtA4PkFgnbuA==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=18"
-      }
-    },
     "node_modules/lint-staged/node_modules/emoji-regex": {
       "version": "10.3.0",
       "resolved": "https://registry.npmjs.org/emoji-regex/-/emoji-regex-10.3.0.tgz",
diff --git a/package.json b/package.json
index 83ea4663..7f79f107 100644
--- a/package.json
+++ b/package.json
@@ -34,6 +34,7 @@
     "@jspsych/plugin-instructions": "^1.1.3",
     "@jspsych/plugin-preload": "^1.1.2",
     "@jspsych/plugin-survey": "^1.0.1",
+    "commander": "^12.1.0",
     "electron-log": "^5.0.0",
     "electron-squirrel-startup": "^1.0.0",
     "firebase": "^10.11.0",