diff --git a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/email/email_params.test.tsx b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/email/email_params.test.tsx
index 3cd54b58bf29a..1020b784f3c58 100644
--- a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/email/email_params.test.tsx
+++ b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/email/email_params.test.tsx
@@ -33,4 +33,97 @@ describe('EmailParamsFields renders', () => {
     expect(wrapper.find('[data-test-subj="subjectInput"]').length > 0).toBeTruthy();
     expect(wrapper.find('[data-test-subj="messageTextArea"]').length > 0).toBeTruthy();
   });
+
+  test('message param field is rendered with default value if not set', () => {
+    const actionParams = {
+      cc: [],
+      bcc: [],
+      to: ['test@test.com'],
+      subject: 'test',
+    };
+
+    const editAction = jest.fn();
+    const wrapper = mountWithIntl(
+      <EmailParamsFields
+        actionParams={actionParams}
+        errors={{ to: [], cc: [], bcc: [], subject: [], message: [] }}
+        editAction={editAction}
+        defaultMessage={'Some default message'}
+        index={0}
+      />
+    );
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some default message', 0);
+  });
+
+  test('when the default message changes, so is the underlying message if it was set by the previous default', () => {
+    const actionParams = {
+      cc: [],
+      bcc: [],
+      to: ['test@test.com'],
+      subject: 'test',
+    };
+
+    const editAction = jest.fn();
+    const wrapper = mountWithIntl(
+      <EmailParamsFields
+        actionParams={actionParams}
+        errors={{ to: [], cc: [], bcc: [], subject: [], message: [] }}
+        editAction={editAction}
+        defaultMessage={'Some default message'}
+        index={0}
+      />
+    );
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some default message', 0);
+
+    wrapper.setProps({
+      defaultMessage: 'Some different default message',
+    });
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some different default message', 0);
+  });
+
+  test('when the default message changes, it doesnt change the underlying message if it wasnt set by a previous default', () => {
+    const actionParams = {
+      cc: [],
+      bcc: [],
+      to: ['test@test.com'],
+      subject: 'test',
+    };
+
+    const editAction = jest.fn();
+    const wrapper = mountWithIntl(
+      <EmailParamsFields
+        actionParams={actionParams}
+        errors={{ to: [], cc: [], bcc: [], subject: [], message: [] }}
+        editAction={editAction}
+        defaultMessage={'Some default message'}
+        index={0}
+      />
+    );
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some default message', 0);
+
+    // simulate value being updated
+    const valueToSimulate = 'some new value';
+    wrapper
+      .find('[data-test-subj="messageTextArea"]')
+      .first()
+      .simulate('change', { target: { value: valueToSimulate } });
+    expect(editAction).toHaveBeenCalledWith('message', valueToSimulate, 0);
+    wrapper.setProps({
+      actionParams: {
+        ...actionParams,
+        message: valueToSimulate,
+      },
+    });
+
+    // simulate default changing
+    wrapper.setProps({
+      defaultMessage: 'Some different default message',
+    });
+
+    expect(editAction).not.toHaveBeenCalledWith('message', 'Some different default message', 0);
+  });
 });
diff --git a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.test.tsx b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.test.tsx
index 0552a126ca66f..86dd304bf6b12 100644
--- a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.test.tsx
+++ b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.test.tsx
@@ -9,8 +9,8 @@ import { ServerLogLevelOptions } from '.././types';
 import ServerLogParamsFields from './server_log_params';
 
 describe('ServerLogParamsFields renders', () => {
-  const editAction = jest.fn();
   test('all params fields is rendered', () => {
+    const editAction = jest.fn();
     const actionParams = {
       level: ServerLogLevelOptions.TRACE,
       message: 'test',
@@ -35,20 +35,103 @@ describe('ServerLogParamsFields renders', () => {
   test('level param field is rendered with default value if not selected', () => {
     const actionParams = {
       message: 'test message',
-      level: ServerLogLevelOptions.INFO,
     };
+    const editAction = jest.fn();
+
+    mountWithIntl(
+      <ServerLogParamsFields
+        actionParams={actionParams}
+        errors={{ message: [] }}
+        editAction={editAction}
+        index={0}
+      />
+    );
+
+    expect(editAction).toHaveBeenCalledWith('level', 'info', 0);
+  });
+
+  test('message param field is rendered with default value if not set', () => {
+    const actionParams = {
+      level: ServerLogLevelOptions.TRACE,
+    };
+
+    const editAction = jest.fn();
+
+    mountWithIntl(
+      <ServerLogParamsFields
+        actionParams={actionParams}
+        defaultMessage={'Some default message'}
+        errors={{ message: [] }}
+        editAction={editAction}
+        index={0}
+      />
+    );
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some default message', 0);
+  });
+
+  test('when the default message changes, so is the underlying message if it was set by the previous default', () => {
+    const actionParams = {
+      level: ServerLogLevelOptions.TRACE,
+    };
+
+    const editAction = jest.fn();
     const wrapper = mountWithIntl(
       <ServerLogParamsFields
         actionParams={actionParams}
+        defaultMessage={'Some default message'}
         errors={{ message: [] }}
-        editAction={() => {}}
+        editAction={editAction}
         index={0}
       />
     );
-    expect(wrapper.find('[data-test-subj="loggingLevelSelect"]').length > 0).toBeTruthy();
-    expect(
-      wrapper.find('[data-test-subj="loggingLevelSelect"]').first().prop('value')
-    ).toStrictEqual('info');
-    expect(wrapper.find('[data-test-subj="messageTextArea"]').length > 0).toBeTruthy();
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some default message', 0);
+
+    wrapper.setProps({
+      defaultMessage: 'Some different default message',
+    });
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some different default message', 0);
+  });
+
+  test('when the default message changes, it doesnt change the underlying message if it wasnt set by a previous default', () => {
+    const actionParams = {
+      level: ServerLogLevelOptions.TRACE,
+    };
+
+    const editAction = jest.fn();
+    const wrapper = mountWithIntl(
+      <ServerLogParamsFields
+        actionParams={actionParams}
+        defaultMessage={'Some default message'}
+        errors={{ message: [] }}
+        editAction={editAction}
+        index={0}
+      />
+    );
+
+    expect(editAction).toHaveBeenCalledWith('message', 'Some default message', 0);
+
+    // simulate value being updated
+    const valueToSimulate = 'some new value';
+    wrapper
+      .find('[data-test-subj="messageTextArea"]')
+      .first()
+      .simulate('change', { target: { value: valueToSimulate } });
+    expect(editAction).toHaveBeenCalledWith('message', valueToSimulate, 0);
+    wrapper.setProps({
+      actionParams: {
+        ...actionParams,
+        message: valueToSimulate,
+      },
+    });
+
+    // simulate default changing
+    wrapper.setProps({
+      defaultMessage: 'Some different default message',
+    });
+
+    expect(editAction).not.toHaveBeenCalledWith('message', 'Some different default message', 0);
   });
 });
diff --git a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.tsx b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.tsx
index ea734439ef41a..ce426c72b64b4 100644
--- a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.tsx
+++ b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/server_log/server_log_params.tsx
@@ -10,9 +10,9 @@ import { ActionParamsProps } from '../../../../types';
 import { ServerLogActionParams } from '.././types';
 import { TextAreaWithMessageVariables } from '../../text_area_with_message_variables';
 
-export const ServerLogParamsFields: React.FunctionComponent<ActionParamsProps<
-  ServerLogActionParams
->> = ({ actionParams, editAction, index, errors, messageVariables, defaultMessage }) => {
+export const ServerLogParamsFields: React.FunctionComponent<
+  ActionParamsProps<ServerLogActionParams>
+> = ({ actionParams, editAction, index, errors, messageVariables, defaultMessage }) => {
   const { message, level } = actionParams;
   const levelOptions = [
     { value: 'trace', text: 'Trace' },
@@ -23,7 +23,7 @@ export const ServerLogParamsFields: React.FunctionComponent<ActionParamsProps<
     { value: 'fatal', text: 'Fatal' },
   ];
   useEffect(() => {
-    if (!actionParams?.level) {
+    if (!actionParams.level) {
       editAction('level', 'info', index);
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps
diff --git a/x-pack/plugins/triggers_actions_ui/public/types.ts b/x-pack/plugins/triggers_actions_ui/public/types.ts
index be8b7b9757e9e..a4eac1ab1da21 100644
--- a/x-pack/plugins/triggers_actions_ui/public/types.ts
+++ b/x-pack/plugins/triggers_actions_ui/public/types.ts
@@ -48,7 +48,7 @@ export interface ActionConnectorFieldsProps<TActionConnector> {
 }
 
 export interface ActionParamsProps<TParams> {
-  actionParams: TParams;
+  actionParams: Partial<TParams>;
   index: number;
   editAction: (key: string, value: AlertActionParam, index: number) => void;
   errors: IErrorObject;