Melling was last seen on stage in When Did You Last See My Mother? at Trafalgar Studios, while other credits include The School for Scandal at the Barbican and Mother Courage and Women Beware Women both at the National Theatre.
The rest of the cast are confirmed as Rebecca Humphries (Sally Bowles), Freddie Capper (Fritz Wendel), Rosemary Smith (Fraulein Schneider), Sherry Baines (Mrs Watson-Courtneidge) and Oliver Rix (Clive Mortimer).
Based on Isherwood's memoirs Goodbye to Berlin, and the inspiration for the musical Cabaret, I am a Camera, by John Van Druten, is part glamorous whirlwind of Berlin Bohemia, part harrowing depiction of the Nazi's rise to power.
They join Owain Arthur who plays lovable chancer Francis Henshall (the role created by Whatsonstage.com and Tony Award-winner James Corden), Jodie Prenger who plays Dolly, Martin Barrass as Alfie, David Benson as Gareth, Nigel Betts as Harry, Derek Elroy as Lloyd, Daniel Ings as Alan, Ben Mansfield as Stanley Stubbers and Gemma Whelan as Rachel Crabbe.
Gavin Spokes will join ensemble members Robin Berry, Gillian Budd, Andrew Dennis, Laura Matthews and Richard Shanks.