diff --git a/docs/api/alerts/find.asciidoc b/docs/api/alerts/find.asciidoc
index 97cd9f4c19ba7..ebd1c7841206c 100644
--- a/docs/api/alerts/find.asciidoc
+++ b/docs/api/alerts/find.asciidoc
@@ -49,6 +49,8 @@ Retrieve a paginated set of alerts based on condition.
 NOTE: As alerts change in {kib}, the results on each page of the response also
 change. Use the find API for traditional paginated results, but avoid using it to export large amounts of data.
 
+NOTE: Alert `params` are stored as {ref}/flattened.html[flattened] and analyzed as `keyword`.
+
 [[alerts-api-find-request-codes]]
 ==== Response code
 
diff --git a/src/core/server/saved_objects/service/lib/filter_utils.test.ts b/src/core/server/saved_objects/service/lib/filter_utils.test.ts
index 05a936db4bfee..92012bf477b3e 100644
--- a/src/core/server/saved_objects/service/lib/filter_utils.test.ts
+++ b/src/core/server/saved_objects/service/lib/filter_utils.test.ts
@@ -76,6 +76,9 @@ const mockMappings = {
             },
           },
         },
+        params: {
+          type: 'flattened',
+        },
       },
     },
     hiddenType: {
@@ -168,6 +171,12 @@ describe('Filter Utils', () => {
       ).toEqual(esKuery.fromKueryExpression('alert.actions:{ actionTypeId: ".server-log" }'));
     });
 
+    test('Assemble filter for flattened fields', () => {
+      expect(
+        validateConvertFilterToKueryNode(['alert'], 'alert.attributes.params.foo:bar', mockMappings)
+      ).toEqual(esKuery.fromKueryExpression('alert.params.foo:bar'));
+    });
+
     test('Lets make sure that we are throwing an exception if we get an error', () => {
       expect(() => {
         validateConvertFilterToKueryNode(
diff --git a/src/core/server/saved_objects/service/lib/filter_utils.ts b/src/core/server/saved_objects/service/lib/filter_utils.ts
index 54b0033c9fcbe..688b7ad96e8ed 100644
--- a/src/core/server/saved_objects/service/lib/filter_utils.ts
+++ b/src/core/server/saved_objects/service/lib/filter_utils.ts
@@ -207,23 +207,33 @@ export const hasFilterKeyError = (
 
 export const fieldDefined = (indexMappings: IndexMapping, key: string): boolean => {
   const mappingKey = 'properties.' + key.split('.').join('.properties.');
-  const potentialKey = get(indexMappings, mappingKey);
+  if (get(indexMappings, mappingKey) != null) {
+    return true;
+  }
 
-  // If the `mappingKey` does not match a valid path, before returning null,
+  // If the `mappingKey` does not match a valid path, before returning false,
   // we want to check and see if the intended path was for a multi-field
   // such as `x.attributes.field.text` where `field` is mapped to both text
   // and keyword
-  if (potentialKey == null) {
-    const propertiesAttribute = 'properties';
-    const indexOfLastProperties = mappingKey.lastIndexOf(propertiesAttribute);
-    const fieldMapping = mappingKey.substr(0, indexOfLastProperties);
-    const fieldType = mappingKey.substr(
-      mappingKey.lastIndexOf(propertiesAttribute) + `${propertiesAttribute}.`.length
-    );
-    const mapping = `${fieldMapping}fields.${fieldType}`;
-
-    return get(indexMappings, mapping) != null;
-  } else {
+  const propertiesAttribute = 'properties';
+  const indexOfLastProperties = mappingKey.lastIndexOf(propertiesAttribute);
+  const fieldMapping = mappingKey.substr(0, indexOfLastProperties);
+  const fieldType = mappingKey.substr(
+    mappingKey.lastIndexOf(propertiesAttribute) + `${propertiesAttribute}.`.length
+  );
+  const mapping = `${fieldMapping}fields.${fieldType}`;
+  if (get(indexMappings, mapping) != null) {
     return true;
   }
+
+  // If the path is for a flattned type field, we'll assume the mappings are defined.
+  const keys = key.split('.');
+  for (let i = 0; i < keys.length; i++) {
+    const path = `properties.${keys.slice(0, i + 1).join('.properties.')}`;
+    if (get(indexMappings, path)?.type === 'flattened') {
+      return true;
+    }
+  }
+
+  return false;
 };
diff --git a/x-pack/plugins/alerts/server/saved_objects/mappings.json b/x-pack/plugins/alerts/server/saved_objects/mappings.json
index f0c5c28ecaeaf..136dc530aa119 100644
--- a/x-pack/plugins/alerts/server/saved_objects/mappings.json
+++ b/x-pack/plugins/alerts/server/saved_objects/mappings.json
@@ -47,8 +47,7 @@
         }
       },
       "params": {
-        "enabled": false,
-        "type": "object"
+        "type": "flattened"
       },
       "scheduledTaskId": {
         "type": "keyword"
diff --git a/x-pack/test/alerting_api_integration/spaces_only/tests/alerting/find.ts b/x-pack/test/alerting_api_integration/spaces_only/tests/alerting/find.ts
index 2b0ff37b62272..1493c99162bf5 100644
--- a/x-pack/test/alerting_api_integration/spaces_only/tests/alerting/find.ts
+++ b/x-pack/test/alerting_api_integration/spaces_only/tests/alerting/find.ts
@@ -19,6 +19,16 @@ export default function createFindTests({ getService }: FtrProviderContext) {
 
     afterEach(() => objectRemover.removeAll());
 
+    async function createAlert(overwrites = {}) {
+      const { body: createdAlert } = await supertest
+        .post(`${getUrlPrefix(Spaces.space1.id)}/api/alerts/alert`)
+        .set('kbn-xsrf', 'foo')
+        .send(getTestAlertData(overwrites))
+        .expect(200);
+      objectRemover.add(Spaces.space1.id, createdAlert.id, 'alert', 'alerts');
+      return createdAlert;
+    }
+
     it('should handle find alert request appropriately', async () => {
       const { body: createdAlert } = await supertest
         .post(`${getUrlPrefix(Spaces.space1.id)}/api/alerts/alert`)
@@ -85,5 +95,23 @@ export default function createFindTests({ getService }: FtrProviderContext) {
           data: [],
         });
     });
+
+    it('should filter on string parameters', async () => {
+      await Promise.all([
+        createAlert({ params: { strValue: 'my a' } }),
+        createAlert({ params: { strValue: 'my b' } }),
+        createAlert({ params: { strValue: 'my c' } }),
+      ]);
+
+      const response = await supertest.get(
+        `${getUrlPrefix(
+          Spaces.space1.id
+        )}/api/alerts/_find?filter=alert.attributes.params.strValue:"my b"`
+      );
+
+      expect(response.status).to.eql(200);
+      expect(response.body.total).to.equal(1);
+      expect(response.body.data[0].params.strValue).to.eql('my b');
+    });
   });
 }