SQL Server Agent - Service Failed to Start (Access is Denied) I have a server running Server 2012 R2 with SQL Server 2012 installed. The SQL Server Agent works fine if it is running under Local System. I changed the SQL Agent service account to a domain account and the service will not start. Checking the event viewer the only error message available is the one below. 


  The SQL Server Agent (NEPO) service failed to start due to the
  following error:  Access is denied.


If I add the domain account to the local admin group on the server the service starts normally. I don't want to leave that account as a local admin. I have also gone through and manually granted all the permissions Microsoft outlines in this article. Still getting the same error and not sure where to turn next.
I hope you are using Configuration Manager to change the Service account.Using the service.msc applet does not grant required permission

Refer the link : https://social.msdn.microsoft.com/Forums/sqlserver/en-US/975c86b9-3622-418a-8e19-6720a51d7549/access-denied-starting-sql-server-agent?forum=sqlgetstarted

Other way could be to add the Service account in SQL Server as sysadmin and then configure it to run under the required service account.