The former 8 out of 10 Cats comedian has been performing in the musical at London's Adelphi Theatre as Italian barber Adolfo Pirelli, the role played by Sacha Baron Cohen in Tim Burton's 2007 movie.
Manford made his first appearance alongside Michael Ball (Sweeney Todd) and Harry Potter's Imelda Staunton (Mrs Lovett) on Monday (July 2).
He will perform in the Stephen Sondheim production until July 27 as a replacement for Robert Burt, who is scheduled to sing at this year's Glyndebourne Festival Opera.
"I'm excited to be making my musical theatre debut in London's West End," Manford said. "It's an absolute honour to join legendary actors Michael Ball and Imelda Staunton as well as such a bloody brilliant company of performers."
He further jested: "Anyone that's wondering what a comedian is doing singing in the West End should remember that once upon a time Frank Spencer became the Phantom - this is the West End, where anything can happen."
Sweeney Todd is scheduled to run until September 22.