Martha and Logan were joined by the Radio 5 Live breakfast co-host and occasional musician on Wednesday evening's event at London's Musicroom store on Denmark Street.
Campbell joined the two-piece when they covered one of his songs as part of their four-track set.
Martha and Logan also played Carly Rae Jepsen's 'Call Me Maybe', Cee Lo Green's 'Forget You' and Adele's 'Rolling In The Deep'.
The duo then gave the crowd a ukulele each and a short tutorial before a mass run-through of Maroon 5's hit 'Moves Like Jagger'.
The Ukuleles is released on August 27 and features ukulele workings of old and new songs, including Jessie J's 'Price Tag', Mumford & Sons' 'The Cave', 'Over The Rainbow' and others.
Watch The Ukuleles' album sampler music video below: