The Letterkenny based Councillor was elected unopposed at today's Annual General Meeting in Lifford as part of an inter-party pact.
He succeeds Cllr John Campbell.
While he has been Mayor of Letterkenny on two occasions, this is the first time Cllr Brogan has been the county's first citizen.
Veteran Donegal politician Cllr Sean McEniff is the new Deputy Mayor.
Speaking to Highland Radio News, the Mayor Cllr Ciaran Brogan says it's a proud day: