Matlock left the Sex Pistols in late February 1977, the legend being that he was 'thrown out' because he "liked the Beatles." Although Matlock has said that one of his biggest influences is the Faces, the Beatles anecdote is fictional. A claim made by the Pistols guitarist Steve Jones, regarding how he thought it was bizarre that Matlock was "always washing his feet", has also been misquoted and misinterpreted as the cause of Matlock's firing from the group. In his autobiography, I Was a Teenage Sex Pistol, Matlock stated that he left the band of his own volition as he was "sick of all the bullshit". In the 2000 documentary The Filth and the Fury, the band members generally agree that there was tension between Matlock and Rotten, which Matlock suggests was exacerbated by Malcolm McLaren's attempts to pit the two men against each other. Matlock was replaced by Sid Vicious, and went on to form The Rich Kids, a New Wave power pop band, with himself as bass guitarist and singer, Midge Ure (guitarist, singer and keyboard player), Steve New (guitarist and singer) and Rusty Egan (drummer). After The Rich Kids he formed The Spectres with Tom Robinson Band guitarist Danny Kustow, and subsequently Mick Hanson, and then Hot Club in 1982 with guitarist James Stevenson and singer Steve Allen.
In John Lydon's autobiography, Rotten: No Blacks, No Dogs, No Irish, Lydon claimed that Matlock worked on later Sex Pistols material (including their album Never Mind the Bollocks, Here's the Sex Pistols) as a paid session musician (Jones played bass on all of the songs recorded after Matlock's departure, with Vicious also contributing to the song "Bodies"). Matlock later played bass with Vicious in the short lived band Vicious White Kids. Matlock also played bass on the Iggy Pop album Soldier and the Damned album Not of This Earth.
Matlock rejoined the original Sex Pistols members for reunion tours in 1996, 2002 and 2003, 2007 and 2008. He played bass guitar and sang for a time in the bands The Philistines and The Flying Padovanis. He toured with a loose collective of punk and post-punk stars, Dead Men Walking, which included Mike Peters of The Alarm, Kirk Brandon of Theatre of Hate and Spear of Destiny, and Pete Wylie of Wah! He now is a member of Slinky Vagabond with Earl Slick, Clem Burke, and Keanan Duffty. Slinky Vagabond played their debut concert at the Joey Ramone Birthday Bash in May 2007. One newspaper wrote, comparing the current lifestyles of the Sex Pistols: "Only original bassist Glen Matlock remains touring with his own band, an irony given that he was sacked for being too conservative..."
In January 2010, Glen Matlock reformed the Rich Kids, for a one-off benefit concert in aid of Steve New. He was joined on stage by original members Rusty Egan and Midge Ure, as well as Mick Jones of The Clash and Gary Kemp from Spandau Ballet. New died of cancer on 24 May 2010.
Matlock joined a reformed Faces, playing at the Vintage at Goodwood festival near Chichester in August 2010. In April 2011 he stood in for Mani playing bass for Primal Scream at the Japan Tsunami appeal concert at Brixton Academy in London.
On 27 November 2011 The International Swingers, a band comprising Glen Matlock, Clem Burke (of Blondie and Romantics), James Stevenson (Gene Loves Jezebel, Chelsea, The Alarm), Gary Twinn (Supernaut, Twenty Flight Rockers), played a warmup gig in LA before a 10 date tour of Australia.