diff --git a/testing/e2e/scaffold/scaffold.go b/testing/e2e/scaffold/scaffold.go
index 8b40f77b28..2998d97fe6 100644
--- a/testing/e2e/scaffold/scaffold.go
+++ b/testing/e2e/scaffold/scaffold.go
@@ -228,14 +228,14 @@ func (s *Scaffold) FleetServerStatusCondition(ctx context.Context, url string, c
 	}
 }
 
-// AgentIsOnline will check Kibana if the agent specified by the passed id has the online status.
+// AgentIsOnline polls Kibana's Fleet API until the agent with the given ID has the online status.
 // The test is marked as failed if the passed context terminates before that.
 func (s *Scaffold) AgentIsOnline(ctx context.Context, id string) {
 	timer := time.NewTimer(time.Second)
 	for {
 		select {
 		case <-ctx.Done():
-			s.Require().NoError(ctx.Err(), "context expired before agent reported online")
+			s.Require().NoError(ctx.Err(), "context expired before agent reached expected status")
 			return
 		case <-timer.C:
 			req, err := http.NewRequestWithContext(ctx, "GET", "http://localhost:5601/api/fleet/agents/"+id, nil)
@@ -308,9 +308,49 @@ type KibanaAgent struct {
 }
 
 type ESAgentDoc struct {
-	Revision      int    `json:"policy_revision_idx"`
-	PolicyID      string `json:"policy_id"`
-	AgentPolicyID string `json:"agent_policy_id"`
+	Revision      int      `json:"policy_revision_idx"`
+	PolicyID      string   `json:"policy_id"`
+	AgentPolicyID string   `json:"agent_policy_id"`
+	Type          string   `json:"type"`
+	Status        string   `json:"status"`
+	Tags          []string `json:"tags"`
+	Agent         struct {
+		ID      string `json:"id"`
+		Version string `json:"version"`
+		Type    string `json:"type"`
+	} `json:"agent"`
+}
+
+func (s *Scaffold) WaitForAgentDoc(ctx context.Context, id string) ESAgentDoc {
+	timer := time.NewTimer(time.Second)
+	for {
+		select {
+		case <-ctx.Done():
+			s.Require().NoError(ctx.Err(), "context expired before agent document appeared in .fleet-agents")
+			return ESAgentDoc{}
+		case <-timer.C:
+			req, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://localhost:9200/.fleet-agents/_doc/"+id, nil)
+			s.Require().NoError(err)
+			req.SetBasicAuth(s.ElasticUser, s.ElasticPass)
+			resp, err := s.Client.Do(req)
+			if err != nil {
+				timer.Reset(time.Second)
+				continue
+			}
+			if resp.StatusCode != http.StatusOK {
+				resp.Body.Close()
+				timer.Reset(time.Second)
+				continue
+			}
+			var obj struct {
+				Source ESAgentDoc `json:"_source"`
+			}
+			err = json.NewDecoder(resp.Body).Decode(&obj)
+			resp.Body.Close()
+			s.Require().NoError(err)
+			return obj.Source
+		}
+	}
 }
 
 func (s *Scaffold) GetAgent(ctx context.Context, id string) ESAgentDoc {
diff --git a/testing/e2e/stand_alone_test.go b/testing/e2e/stand_alone_test.go
index 3a37dac034..dde0e7a1b5 100644
--- a/testing/e2e/stand_alone_test.go
+++ b/testing/e2e/stand_alone_test.go
@@ -579,3 +579,132 @@ func (suite *StandAloneSuite) TestAPMInstrumentation() {
 	cancel()
 	cmd.Wait()
 }
+
+// TestOpAMP ensures that the OpAMP endpoint in Fleet Server works as expected by installing
+// an OTel Collector, configuring it with the OpAMP extension, and having it connect to Fleet
+// Server using OpAMP, and verifying that Fleet Server responds to this request with an HTTP
+// 200 OK status response.
+func (suite *StandAloneSuite) TestOpAMP() {
+	// Create a config file from a template in the test temp dir
+	dir := suite.T().TempDir()
+	tpl, err := template.ParseFiles(filepath.Join("testdata", "stand-alone-opamp.tpl"))
+	suite.Require().NoError(err)
+	f, err := os.Create(filepath.Join(dir, "config.yml"))
+	suite.Require().NoError(err)
+	err = tpl.Execute(f, map[string]interface{}{
+		"Hosts":          suite.ESHosts,
+		"ServiceToken":   suite.ServiceToken,
+		"StaticTokenKey": "opamp-e2e-test-key",
+	})
+	f.Close()
+	suite.Require().NoError(err)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
+	defer cancel()
+
+	// Run the fleet-server binary
+	cmd := exec.CommandContext(ctx, suite.binaryPath, "-c", filepath.Join(dir, "config.yml"))
+	cmd.Cancel = func() error {
+		return cmd.Process.Signal(syscall.SIGTERM)
+	}
+	cmd.Env = []string{"GOCOVERDIR=" + suite.CoverPath}
+	err = cmd.Start()
+	suite.Require().NoError(err)
+	defer cmd.Wait()
+
+	suite.FleetServerStatusOK(ctx, "http://localhost:8220")
+
+	apiKey := suite.GetEnrollmentTokenForPolicyID(ctx, "dummy-policy")
+
+	// Make sure the OpAMP endpoint works.
+	req, err := http.NewRequestWithContext(ctx, "POST", "http://localhost:8220/v1/opamp", nil)
+	suite.Require().NoError(err)
+	req.Header.Set("Authorization", "ApiKey "+apiKey)
+	req.Header.Set("Content-Type", "application/x-protobuf")
+
+	resp, err := suite.Client.Do(req)
+	suite.Require().NoError(err)
+	resp.Body.Close()
+	suite.Require().Equal(http.StatusOK, resp.StatusCode)
+
+	// Enroll a dummy agent to initialize the .fleet-agents index before the OTel Collector connects.
+	// Without this, findEnrolledAgent fails with index_not_found_exception when the OTel Collector
+	// sends its first AgentToServer message, because .fleet-agents doesn't exist yet in a fresh
+	// standalone fleet-server environment (unlike agent-managed fleet-server which self-enrolls).
+	tester := api_version.NewClientAPITesterCurrent(suite.Scaffold, "http://localhost:8220", apiKey)
+	tester.Enroll(ctx, apiKey)
+
+	// Clone OTel Collector contrib repository (shallow clone of main branch)
+	cloneDir := filepath.Join(dir, "opentelemetry-collector-contrib")
+	suite.T().Logf("Cloning opentelemetry-collector-contrib (main) to %s", cloneDir)
+	cloneCmd := exec.CommandContext(ctx,
+		"git", "clone",
+		"--depth", "1",
+		"https://github.com/open-telemetry/opentelemetry-collector-contrib",
+		cloneDir,
+	)
+	cloneCmd.Stdout = os.Stdout
+	cloneCmd.Stderr = os.Stderr
+	err = cloneCmd.Run()
+	suite.Require().NoError(err)
+
+	// Build the OTel Collector binary
+	suite.T().Log("Building otelcol-contrib binary via make otelcontribcol")
+	makeCmd := exec.CommandContext(ctx, "make", "otelcontribcol")
+	makeCmd.Dir = cloneDir
+	makeCmd.Stdout = os.Stdout
+	makeCmd.Stderr = os.Stderr
+	err = makeCmd.Run()
+	suite.Require().NoError(err)
+
+	// The make target places the binary under bin/; move it to the expected path.
+	builtBinary := filepath.Join(cloneDir, "bin", fmt.Sprintf("otelcontribcol_%s_%s", runtime.GOOS, runtime.GOARCH))
+	otelBinaryPath := filepath.Join(dir, "otelcol-contrib")
+	err = os.Rename(builtBinary, otelBinaryPath)
+	suite.Require().NoError(err)
+
+	// Configure it with the OpAMP extension
+	instanceUID := "019b8d7a-2da8-7657-b52d-492a9de33319"
+	suite.T().Logf("Configuring OTel Collector with OpAMP extension (instanceUID=%s)", instanceUID)
+	tpl, err = template.ParseFiles(filepath.Join("testdata", "otelcol-opamp.tpl"))
+	suite.Require().NoError(err)
+	f, err = os.Create(filepath.Join(dir, "otelcol.yml"))
+	suite.Require().NoError(err)
+	err = tpl.Execute(f, map[string]interface{}{
+		"OpAMP": map[string]string{
+			"InstanceUID": instanceUID,
+			"APIKey":      apiKey,
+		},
+	})
+	f.Close()
+	suite.Require().NoError(err)
+
+	// Start OTel Collector
+	suite.T().Log("Starting OTel Collector")
+	otelCmd := exec.CommandContext(ctx, otelBinaryPath, "--config", filepath.Join(dir, "otelcol.yml"))
+	otelCmd.Cancel = func() error {
+		return otelCmd.Process.Signal(syscall.SIGTERM)
+	}
+	otelCmd.Stdout = os.Stdout
+	otelCmd.Stderr = os.Stderr
+	err = otelCmd.Start()
+	suite.Require().NoError(err)
+	defer otelCmd.Wait()
+
+	// Verify that the OTel Collector was enrolled in Fleet by fetching its document from
+	// .fleet-agents and asserting on its contents.
+	suite.T().Logf("Waiting for agent %s to appear in .fleet-agents", instanceUID)
+	agentDoc := suite.WaitForAgentDoc(ctx, instanceUID)
+
+	suite.Equal(instanceUID, agentDoc.Agent.ID, "expected agent.id to match instanceUID")
+	// TODO: uncomment once https://github.com/elastic/fleet-server/pull/6400 is merged
+	// versionOut, err := exec.Command(otelBinaryPath, "--version").Output()
+	// suite.Require().NoError(err)
+	// otelVersion := strings.TrimPrefix(strings.TrimSpace(string(versionOut)), "otelcontribcol version ")
+	// suite.Equal("OPAMP", agentDoc.Type, "expected type to be OPAMP")
+	// suite.Equal("otelcontribcol", agentDoc.Agent.Type, "expected agent.type to be otelcontribcol")
+	// suite.Equal(otelVersion, agentDoc.Agent.Version, "expected agent.version to match otelcol-contrib binary version")
+	// suite.Equal(1, agentDoc.Revision, "expected policy_revision_idx to be 1")
+	// suite.Contains(agentDoc.Tags, "otelcontribcol", "expected tags to contain otelcontribcol")
+	// suite.Equal("online", agentDoc.Status, "expected status to be online")
+}
diff --git a/testing/e2e/testdata/otelcol-opamp.tpl b/testing/e2e/testdata/otelcol-opamp.tpl
new file mode 100644
index 0000000000..0d0ec1896a
--- /dev/null
+++ b/testing/e2e/testdata/otelcol-opamp.tpl
@@ -0,0 +1,27 @@
+receivers:
+  otlp:
+    protocols:
+      grpc:
+        endpoint: 0.0.0.0:4317
+
+exporters:
+  debug:
+    verbosity: detailed
+
+extensions:
+  opamp:
+    server:
+      http:
+        endpoint: http://localhost:8220/v1/opamp
+        tls:
+          insecure: true
+        headers:
+          Authorization: ApiKey {{ .OpAMP.APIKey }}
+    instance_uid: {{ .OpAMP.InstanceUID }}
+
+service:
+  pipelines:
+    logs:
+      receivers: [otlp]
+      exporters: [debug]
+  extensions: [opamp]
\ No newline at end of file
diff --git a/testing/e2e/testdata/stand-alone-opamp.tpl b/testing/e2e/testdata/stand-alone-opamp.tpl
new file mode 100644
index 0000000000..f1f20b42f4
--- /dev/null
+++ b/testing/e2e/testdata/stand-alone-opamp.tpl
@@ -0,0 +1,21 @@
+output:
+  elasticsearch:
+    hosts: {{ .Hosts }}
+    service_token: {{ .ServiceToken }}
+
+fleet.agent.id: e2e-test-id
+
+inputs:
+- type: fleet-server
+  server:
+    feature_flags:
+      enable_opamp: true
+    static_policy_tokens:
+      enabled: true
+      policy_tokens:
+        - token_key: {{ .StaticTokenKey }}
+          policy_id: dummy-policy
+
+logging:
+  to_stderr: true
+