Born in Westcliff-on-Sea, Essex, England, Clement was educated at Bishop's Stortford College, and then spent a year in the US on an exchange visit.
Their partnership began in the mid-1960s with The Likely Lads, and by the end of the decade they had also written three feature films: The Jokers, Otley, (directed by Clement) and Hannibal Brooks.
By this time they were living in California, where they wrote the American version of Porridge, On the Rocks, and the feature film, The Prisoner of Zenda, starring Peter Sellers.
In addition, they did uncredited rewrites on The Rock, starring Sean Connery, and Pearl Harbor for producers Jerry Bruckheimer and Michael Bay (who also directed the film).
This would ultimately lead the film into pre-production after several failed drafts but it was heavily rewritten by Ed Solomon once Walt Disney Studios acquired distribution rights.
In 2006, they were credited as writers on the animated film Flushed Away, whilst 2007 saw the release of the jukebox musical Across the Universe, based around the songs of The Beatles, which they scripted, and, with director Julie Taymor, wrote the story for.