diff --git a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.test.ts b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.test.ts
index dfe0828e88bad..5d65909dde50d 100644
--- a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.test.ts
+++ b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.test.ts
@@ -41,4 +41,16 @@ describe('APM Transaction Duration Transform Generator', () => {
 
     expect(transform.source.query).toMatchSnapshot();
   });
+
+  it('uses the provided index params as source index', async () => {
+    const index = 'my-custom-apm-index*';
+    const anSLO = createSLO({
+      indicator: createAPMTransactionDurationIndicator({
+        index,
+      }),
+    });
+    const transform = generator.getTransformParams(anSLO);
+
+    expect(transform.source.index).toEqual(index);
+  });
 });
diff --git a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.ts b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.ts
index 6cba9c32d40ac..23ee248a1372f 100644
--- a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.ts
+++ b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_duration.ts
@@ -16,8 +16,7 @@ import {
 import { getSLOTransformTemplate } from '../../../assets/transform_templates/slo_transform_template';
 import { SLO, APMTransactionDurationIndicator } from '../../../domain/models';
 import { TransformGenerator } from '.';
-
-const APM_SOURCE_INDEX = 'metrics-apm*';
+import { DEFAULT_APM_INDEX } from './constants';
 
 export class ApmTransactionDurationTransformGenerator extends TransformGenerator {
   public getTransformParams(slo: SLO): TransformPutTransformRequest {
@@ -74,7 +73,7 @@ export class ApmTransactionDurationTransformGenerator extends TransformGenerator
     }
 
     return {
-      index: APM_SOURCE_INDEX,
+      index: indicator.params.index ?? DEFAULT_APM_INDEX,
       runtime_mappings: this.buildCommonRuntimeMappings(slo),
       query: {
         bool: {
diff --git a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.test.ts b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.test.ts
index e44f4be531c32..0960fe7c073ca 100644
--- a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.test.ts
+++ b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.test.ts
@@ -50,4 +50,16 @@ describe('APM Transaction Error Rate Transform Generator', () => {
 
     expect(transform.source.query).toMatchSnapshot();
   });
+
+  it('uses the provided index params as source index', async () => {
+    const index = 'my-custom-apm-index*';
+    const anSLO = createSLO({
+      indicator: createAPMTransactionErrorRateIndicator({
+        index,
+      }),
+    });
+    const transform = generator.getTransformParams(anSLO);
+
+    expect(transform.source.index).toEqual(index);
+  });
 });
diff --git a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.ts b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.ts
index a68eb490ebde1..f0df8dd54209f 100644
--- a/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.ts
+++ b/x-pack/plugins/observability/server/services/slo/transform_generators/apm_transaction_error_rate.ts
@@ -16,8 +16,8 @@ import {
   getSLOTransformId,
 } from '../../../assets/constants';
 import { APMTransactionErrorRateIndicator, SLO } from '../../../domain/models';
+import { DEFAULT_APM_INDEX } from './constants';
 
-const APM_SOURCE_INDEX = 'metrics-apm*';
 const ALLOWED_STATUS_CODES = ['2xx', '3xx', '4xx', '5xx'];
 const DEFAULT_GOOD_STATUS_CODES = ['2xx', '3xx', '4xx'];
 
@@ -76,7 +76,7 @@ export class ApmTransactionErrorRateTransformGenerator extends TransformGenerato
     }
 
     return {
-      index: APM_SOURCE_INDEX,
+      index: indicator.params.index ?? DEFAULT_APM_INDEX,
       runtime_mappings: this.buildCommonRuntimeMappings(slo),
       query: {
         bool: {
diff --git a/x-pack/plugins/observability/server/services/slo/transform_generators/constants.ts b/x-pack/plugins/observability/server/services/slo/transform_generators/constants.ts
new file mode 100644
index 0000000000000..0bd3f7f31edcc
--- /dev/null
+++ b/x-pack/plugins/observability/server/services/slo/transform_generators/constants.ts
@@ -0,0 +1,8 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+export const DEFAULT_APM_INDEX = 'metrics-apm*';
diff --git a/x-pack/plugins/observability/server/types/schema/indicators.ts b/x-pack/plugins/observability/server/types/schema/indicators.ts
index ef7b2d59fcf74..a430ee421a346 100644
--- a/x-pack/plugins/observability/server/types/schema/indicators.ts
+++ b/x-pack/plugins/observability/server/types/schema/indicators.ts
@@ -11,13 +11,18 @@ import { allOrAnyString, dateRangeSchema } from './common';
 const apmTransactionDurationIndicatorTypeSchema = t.literal('sli.apm.transaction_duration');
 const apmTransactionDurationIndicatorSchema = t.type({
   type: apmTransactionDurationIndicatorTypeSchema,
-  params: t.type({
-    environment: allOrAnyString,
-    service: allOrAnyString,
-    transaction_type: allOrAnyString,
-    transaction_name: allOrAnyString,
-    'threshold.us': t.number,
-  }),
+  params: t.intersection([
+    t.type({
+      environment: allOrAnyString,
+      service: allOrAnyString,
+      transaction_type: allOrAnyString,
+      transaction_name: allOrAnyString,
+      'threshold.us': t.number,
+    }),
+    t.partial({
+      index: t.string,
+    }),
+  ]),
 });
 
 const apmTransactionErrorRateIndicatorTypeSchema = t.literal('sli.apm.transaction_error_rate');
@@ -34,6 +39,7 @@ const apmTransactionErrorRateIndicatorSchema = t.type({
       good_status_codes: t.array(
         t.union([t.literal('2xx'), t.literal('3xx'), t.literal('4xx'), t.literal('5xx')])
       ),
+      index: t.string,
     }),
   ]),
 });