Jim Mullen with The Terry Hutchins Qrt

Jim Mullen was guitarist with Pete Brown & Piblokto! for two albums in 1970. He then played with Brian Auger's Oblivion Express, appearing on the band's first three albums together with future Average White Band drummer Robbie McIntosh. Mullen then joined Kokomo and later toured with the Average White Band.

It was while both musicians were touring the United States with AWB in the mid-1970s that Mullen met tenor saxophone player Dick Morrissey and throughout the 1980s, he found critical notice as joint leader of the British jazz funk band Morrissey–Mullen. Record producer Richard Niles, who produced the band's sixth album, It's About Time, later produced three solo albums for Mullen.

Mullen has also played and recorded with, among others, Mose Allison, Hamish Stuart, Joanna Eden, Tam White, Claire Martin, Mike Carr, Jimmy Witherspoon, Dave O'Higgins and Georgie Fame, Sinan Alimanović, David Tughan, Jimmy Smith, Terry Callier and Frank Holder. Mullen has recorded as part of The AllStars, a collective of session musicians on their Paul McCartney-produced album All About the Music, alongside special guests Jocelyn Brown, Hamish Stuart and Angelo Starr. In 2014, he featured prominently on the Citrus Sun album, People of Tomorrow, produced by Incognito co-founder, Jean-Paul 'Bluey' Maunick.

Mullen has won many British music awards including "Best Guitar" in the British Telecom Jazz Awards (1994, 1996 and 2000).