The comedian and former One Show host will make his stage debut with a guest stint as Italian barber Adolfo Pirelli, a role made famous by Sacha Baron Cohen in the Tim Burton 2007 film.
Manford will appear in the show at London's Adelphi theatre between July 2 and 27, according to the BBC.
Michael Ball stars as the titular villain, while Harry Potter actress Imelda Staunton portrays his partner-in-crime Mrs Lovett. The roles were taken on by Johnny Depp and Helena Bonham Carter in the big-screen adaptation.
Previews of Sweeney Todd are being held this weekend and the show begins on March 20.
The revival of Stephen Sondheim's musical is produced by Jonathan Kent and opened at the Chichester Festival Theatre last year.
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Watch Sacha Baron Cohen as Adolfo Pirelli in Sweeney Todd: The Demon Barber Of Fleet Street below: