John Clarke was the second Mayor of Belfast, under the new Act. He was active in the public life of the city, and for many years served as Chairman of the Belfast Harbour Commission and as a Justice of the Peace.

Clarke was also involved in many philanthropic organisations and was a member of the Belfast Charitable Society (Clifton House) and served on the board of the Brown Street School. He was a proprietor of the Botanic Gardens supporter of the Linen Hall Library.

Clarke lived at College Square in the city, and died aged seventy.