Frinton was born in Hainton Avenue, Grimsby, Lincolnshire, the illegitimate child of a seamstress, Florence Elisabeth Coo, and was brought up by foster parents. He started working in a Grimsby fish processing plant, where he is said to have entertained his colleagues with parodies and jokes, but was ultimately sacked.

He moved into music hall, where he enjoyed modest success and renamed himself Freddie Frinton. During the Second World War he made a moderate breakthrough as a comedian. In 1945, Frinton first performed the sketch Dinner for One in Blackpool.