Frisby was born in 1932 in New Cross, south east London and educated at Dartford Grammar School. He is father of stand-up comedian and voice-over artist Dominic Frisby.
There's A Girl in My Soup opened in 1966 at the Globe Theatre (now called the Gielgud Theatre) and ran for over 1,000 performances, becoming a worldwide hit with runs on Broadway, Paris (with Gérard Depardieu), Berlin, Stockholm, Sydney, Rome (starring Domenico Modugno), Vienna, Prague and many other places. His script for the equally successful 1970 film, which starred Peter Sellers and Goldie Hawn, won the Writers' Guild of Great Britain Award in 1970 for the Best British Comedy Screenplay.
His other stage plays include The Subtopians (Arts Theatre 1964), The Bandwagon (Mermaid Theatre 1969), It's All Right If I Do It (Mermaid 1977), Seaside Postcard (Young Vic 1978) Rough Justice (Apollo Theatre 1994) Funny About Love (two UK national tours 1999-2000). All his plays are published by Samuel French.
Frisby has also written many plays for television, two of which were nominated for awards. His comedy series include Lucky Feller with David Jason (1976) and That's Love with Jimmy Mulville, Diana Hardcastle, and Tony Slattery (1988–92), which won the Gold Award for Comedy at the 1991 Houston International Film Festival.
His radio play Just Remember Two Things: It's Not Fair And Don't Be Late for BBC Radio Four won The Giles Cooper Award, and a musical stage version was produced at the Queen's Theatre, Barnstaple in 2004 under the title Just Remember Two Things... A second production of the same show, under the title Kisses on a Postcard, was produced in 2011 at the same venue.
His first book was Outrageous Fortune, an autobiographical story about his fifteen years as a litigant-in-person in the High Court following his divorce and custody battle. His second book is Kisses on a Postcard, published by Bloomsbury (ISBN 9781408800584). It tells of his experiences as an evacuee as a 7-year-old from London to Cornwall during World War Two. It is based on the musical of the same name.
Frisby has worked for 40 years as an actor, director and producer. He has played leads and directed in the West End, Young Vic and all over the country. His most noted presentation was the South African, multi-award-winning Woza Albert! at the Criterion Theatre in 1983, subsequently off-Broadway and worldwide.
He was one of the earliest members of the father's rights and support group Families Need Fathers.