Archer joined Oasis as second lead guitarist in November 1999, and contributed to the writing of some of the band's songs.

Archer formed Heavy Stereo with bassist Nez and guitarist Pete Downing both previously of Redcar indie band 2 Lost Sons who were subsequently signed with Creation Records.

Archer heard a report on The Big Breakfast that Paul "Bonehead" Arthurs had left Oasis after a massive row with Noel Gallagher.

He was unaware that Noel Gallagher – who knew Archer from both their days on the Creation Records label – had rung his home in London and invited him to Olympic Studios, where Oasis were mixing Standing on the Shoulder of Giants.

His role was expanded on Oasis' sixth studio album, Don't Believe the Truth, which features Archer's "A Bell Will Ring" and "Love Like a Bomb", the latter of which he co-wrote with singer Liam Gallagher.

Archer, in rare occasions, contributed backing vocals to Oasis songs, such as on "The Meaning of Soul", "Force of Nature", and on the band's cover of The Who's "My Generation", played piano on "Stop Crying Your Heart Out" and harmonica on "Mucky Fingers".

[citation needed] Noel Gallagher quit Oasis in August 2009, following an argument with his brother in Paris.

[5] However, Archer, Bell, Liam Gallagher and Oasis live drummer Chris Sharrock resolved to work together on a new project under a new name, Beady Eye.

Archer contributed guitar, bass and backing vocals to Beady Eye's debut album Different Gear, Still Speeding, released on 28 February 2011.

Archer also contributed guitar, keyboards, and backing vocals on Beady Eye's second album BE, released on 10 June 2013.

In October 2016, Gem joined Noel Gallagher's High Flying Birds for their performance of "Half the World Away" dedicated to Caroline Aherne for Channel 4's Stand Up to Cancer telethon; leading to speculation he had become a permanent member of the band.

According to album notes, Gem also worked with his good friend and previous Oasis and Beady Eye colleague Andy Bell on his debut solo album (not under the “Glok” alias) called “The View from Halfway Down”, contributing some drums, bass and guitar tracks, and also providing some of the recording work.

[11] On 1 August 2013, Archer was admitted to hospital with serious head trauma and a fractured skull after a freak accident at home, by falling down a flight of stairs.