The former leader of Worcestershire County Council is being investigated by police for an alleged sexual offence 30 years ago.
Dr George Lord quit as leader and a Conservative councillor after separate allegations were made that he had acted inappropriately towards staff.
West Mercia Police said it was investigating the alleged historical sexual offence against a woman.
Dr Lord has not commented on Saturday's resignation or any of the allegations.
"As this is now an ongoing police investigation no further information will be given at this stage, including the identities of anyone concerned with the case," a police spokesman added.
Dr Lord had represented the seat for Alvechurch at the local authority.