The core members of the group for most of the band's career were:
* Vivian Stanshall (1943–1995): trumpet, lead vocals
* Neil Innes (b. 1944): piano, guitar, lead vocals
* Rodney "Rhino" Desborough Slater (b. 1944): saxophone
* Roger Ruskin Spear (b. 1943): tenor sax and various contraptions
* "Legs" Larry Smith (b. 1944): drums
However, the band's onstage line-up varied, sometimes on a weekly basis, and they also invited a number of guest musicians into the recording studio. Additional members of various duration include: Vernon Dudley Bohay-Nowell, Martin "Sam Spoons" Ash, "Happy" Wally Wilks, Tom Parkinson, Chris Jennings, Claude Abbo, Trevor Brown, Tom Hedge, Eric Idle, Eric Clapton, Elton John, Paul McCartney, Leon Williams, John Parry, Raymond Lewitt, Sydney "Big Sid" Nicholls, James "Jim Strobes" Chambers, Bob Kerr, Dave Clague, Joel Druckman, "Borneo" Fred Munt, Chalky Chalkey, Dennis Cowan, Aynsley Dunbar, Jim Capaldi, Anthony 'Bubs' White, Andy Roberts, Dave Richards, Pete Currie, Dick Parry, Hughie Flint and Glen Colson.
Stanshall and Innes were the band's principal songwriters. After the band's demise, both became founding members of Grimms along with the members of The Scaffold.