Following a stint in the short-lived Roosters with Eric Clapton, McGuinness joined the 1960s group Manfred Mann as a bassist, performing in a line-up with Paul Jones. As the band sought to transform itself from jazz into a rhythm-and-blues-orientated group, he took over bass duties from Dave Richmond and received joint songwriting credits on the group's early hits. Explaining how he came into the group, McGuinness said, "They had a great bass guitarist, but he was into Charles Mingus and things like that, which the whole band was. But he refused to play simple bass lines that would fit Bo Diddley numbers. He'd play incredible 3/4 lines and things like that. So I came in and I had the overwhelming advantage of not really being able to play the bass guitar, so I played simple."[2] Appointed the writer of album sleeve notes, he took the opportunity to identify himself as "the nastiest in the group".[3]
When Mike Vickers and then Paul Jones left the band, McGuinness took over the guitarist role; Jack Bruce then played bass until replaced by Klaus Voormann. McGuinness' National Steel guitar became an important part of the group's sound, and featured on hits such as "Pretty Flamingo". He composed a few album tracks for the group, notably "L.S.D." (from Mann Made), "One Way", and "Cubist Town" (from Mighty Garvey!).
Their first single "When I'm Dead and Gone" reached No. 2 on the UK Singles Chart at the end of 1970 (losing the number one spot to Clive Dunn's Grandad), No. 47 on the Billboard pop chart and No.3 5 on the Cashbox pop chart in the U.S., No. 5 in Ireland, and No. 31 in Canada.[5][6]) The debut album McGuinness Flint also made the Top 10 of the UK Albums Chart.[7] In 1999, it received another outing, in the soundtrack of the film, East is East. A follow-up single, "Malt and Barley Blues", was a UK No. 5 hit in 1971 and peaked at No.15 in Ireland.[7][8]
The Blues Band and The Manfreds
In 1979, four years after McGuinness Flint split up, both founded The Blues Band. Also including Paul Jones, it went on hiatus in 1983, shortly after recording a live album, and regrouped in 1986. It played its last performance in 2022, soon after releasing the last studio album "So Long".[9]