diff --git a/js/plugins/vertexai/src/gemini.ts b/js/plugins/vertexai/src/gemini.ts
index 797b3c0d9a..6d5e223e9a 100644
--- a/js/plugins/vertexai/src/gemini.ts
+++ b/js/plugins/vertexai/src/gemini.ts
@@ -279,6 +279,61 @@ export function toGeminiMessage(
   };
 }
 
+export function toGeminiMessages(
+  messages: MessageData[],
+  model?: ModelReference<z.ZodTypeAny>
+): Content[] {
+  const geminiMessages: Content[] = [];
+
+  for (let i = 0; i < messages.length; i++) {
+    if (messages[i].content.some((part) => part.toolResponse)) {
+      const toolResponseMessage = messages[i];
+
+      // get the most recent user message in the history
+      const previousUserMessageIndex = messages
+        .slice(0, i)
+        .reverse()
+        .findIndex((m) => m.role === toGeminiRole('user', model));
+
+      if (previousUserMessageIndex === -1) {
+        throw new Error(
+          'Tool response message must be preceded by a user message'
+        );
+      }
+
+      const actualPreviousUserMessageIndex = i - 1 - previousUserMessageIndex;
+      const previousUserMessage = messages[actualPreviousUserMessageIndex];
+
+      const newToolResponseMessage = {
+        role: toGeminiRole(toolResponseMessage.role, model),
+        parts: [toGeminiToolResponsePart(toolResponseMessage.content[0])],
+      };
+
+      const otherParts = toolResponseMessage.content.filter(
+        (part) => !part.toolResponse
+      );
+
+      if (otherParts.length > 0) {
+        const newPreviousUserMessage = {
+          role: toGeminiRole(previousUserMessage.role, model),
+          parts: [...previousUserMessage.content, ...otherParts].map(
+            toGeminiPart
+          ),
+        };
+
+        // Modify geminiMessages in place to replace the previous user message
+        geminiMessages[actualPreviousUserMessageIndex] = newPreviousUserMessage;
+      }
+
+      geminiMessages.push(newToolResponseMessage);
+    } else {
+      geminiMessages.push(toGeminiMessage(messages[i], model));
+    }
+  }
+
+  return geminiMessages;
+}
+
 function fromGeminiFinishReason(
   reason: GenerateContentCandidate['finishReason']
 ): CandidateData['finishReason'] {
@@ -490,14 +545,14 @@ export function geminiModel(name: string, vertex: VertexAI): ModelAction {
         }
       }
 
+      const geminiMessages = toGeminiMessages(messages, model);
+
       const chatRequest: StartChatParams = {
         systemInstruction,
         tools: request.tools?.length
           ? [{ functionDeclarations: request.tools?.map(toGeminiTool) }]
           : [],
-        history: messages
-          .slice(0, -1)
-          .map((message) => toGeminiMessage(message, model)),
+        history: geminiMessages.slice(0, -1),
         generationConfig: {
           candidateCount: request.candidates || undefined,
           temperature: request.config?.temperature,
@@ -508,7 +563,7 @@ export function geminiModel(name: string, vertex: VertexAI): ModelAction {
         },
         safetySettings: request.config?.safetySettings,
       };
-      const msg = toGeminiMessage(messages[messages.length - 1], model);
+      const msg = geminiMessages[geminiMessages.length - 1];
       if (streamingCallback) {
         const result = await client
           .startChat(chatRequest)
diff --git a/js/plugins/vertexai/tests/gemini_test.ts b/js/plugins/vertexai/tests/gemini_test.ts
index dbb39e8f1c..5fe42025e8 100644
--- a/js/plugins/vertexai/tests/gemini_test.ts
+++ b/js/plugins/vertexai/tests/gemini_test.ts
@@ -21,10 +21,11 @@ import { describe, it } from 'node:test';
 import {
   fromGeminiCandidate,
   toGeminiMessage,
+  toGeminiMessages,
   toGeminiSystemInstruction,
 } from '../src/gemini.js';
 
-describe('toGeminiMessages', () => {
+describe('toGeminiMessage', () => {
   const testCases = [
     {
       should: 'should transform genkit message (text content) correctly',
@@ -345,3 +346,79 @@ describe('fromGeminiCandidate', () => {
     });
   }
 });
+
+describe('toGeminiMessages', () => {
+  it('should handle tool request messages correctly', () => {
+    const messages = [
+      {
+        role: 'user',
+        content: [{ text: 'What is the weather like today?.' }],
+      },
+      {
+        role: 'model',
+        content: [
+          {
+            toolRequest: {
+              name: 'tellMeTheWeather',
+              input: { request: 'tell me the weather' },
+            },
+          },
+        ],
+      },
+      {
+        role: 'tool',
+        content: [
+          {
+            toolResponse: {
+              name: 'tellMeTheWeather',
+              output: 'it is sunny today',
+            },
+          },
+          { text: 'This is extra context', metadata: { purpose: 'context' } },
+        ],
+      },
+    ];
+
+    const expectedOutput = [
+      {
+        role: 'user',
+        parts: [
+          {
+            text: 'What is the weather like today?.',
+          },
+          { text: 'This is extra context' },
+        ],
+      },
+      {
+        role: 'model',
+        parts: [
+          {
+            functionCall: {
+              name: 'tellMeTheWeather',
+              args: {
+                request: 'tell me the weather',
+              },
+            },
+          },
+        ],
+      },
+      {
+        role: 'function',
+        parts: [
+          {
+            functionResponse: {
+              name: 'tellMeTheWeather',
+              response: {
+                name: 'tellMeTheWeather',
+                content: 'it is sunny today',
+              },
+            },
+          },
+        ],
+      },
+    ];
+    const output = toGeminiMessages(messages as MessageData[]);
+
+    assert.deepEqual(output, expectedOutput);
+  });
+});