He was born in Boston, Massachusetts, the son of John Gerrish and Sarah Hobbes.

[1] In 1760, he was named justice of the peace for Halifax County, a captain in the militia and Indian commissary.

When Jonathan Belcher became lieutenant governor, he removed Gerrish from the commissary contract.

In 1768, Gerrish was named to the province's Council, resigning his assembly seat on June 27, 1768.

Rebecca, his widow, married John Burbidge, another member of the province's assembly.