[5] In 1965, he was hired, for the sum of £30 a week, to join Small Faces by their manager, Don Arden, replacing Jimmy Winston.

[6] With the band, he wrote and sang only two songs which are credited entirely to him, "Up the Wooden Hills to Bedfordshire" and "Long Agos and Worlds Apart", which appear on Small Faces and Ogdens' Nut Gone Flake respectively.

In 1969, Steve Marriott left the group; Rod Stewart and Ronnie Wood joined, and the band changed its name to Faces.

In addition, his session work has backed such artists as Arc Angels, Chuck Berry, Jackson Browne, Joe Cocker, Bob Dylan,[7] James McMurtry, Melissa Etheridge, Bonnie Raitt, Sid Griffin, Paul Westerberg, Izzy Stradlin, John Hiatt, Frank Black, Nikki Sudden, John Mayer, Bruce Springsteen, Tony Scalzo, Carla Olson, Mick Taylor, and The Georgia Satellites.

He was a member of Billy Bragg's band "The Blokes" for several years in the late 1990s and early 2000s, co-writing and performing on the 2002 England, Half-English album and tour.

[9] On 25 September 2010, at Stubbs in Austin, Texas, McLagan joined The Black Crowes on keyboards and vocals for their encore set.

In 2013, he appeared with the Warren Haynes band at the Moody Theater in Austin, Texas, playing piano on one number and organ on the other.

McLagan is featured prominently on the Lucinda Williams double album Down Where the Spirit Meets the Bone, which was released 30 September 2014 on her own label, Highway 20 Records.

[11] He also features prominently on Scunthorpe duo Ruen Brothers' debut album All My Shades Of Blue, released 1 June 2018 via Ramseur Records.

Other notable musicians on the album were Chad Smith from the Red Hot Chili Peppers and Dave Keuning from the Killers.