In the 1960s he found himself in Dublin, and began an itinerant life of a musician. He found musical influences in the likes of Ewan MacColl (notably the songs he wrote for his radio-ballads), and the Child Ballads. There he met Johnny Moynihan, with whom he formed a musical partnership, which, with the addition of Joe Dolan, turned into Sweeney's Men in 1966.
A year later Dolan departed, and was replaced with Terry Woods (later of Steeleye Span and The Pogues). After recording several singles and an album Irvine left the band, and headed to Eastern Europe (he later wrote a song about his experiences there: "Baneasa's Green Glade", which was recorded years later by Planxty). During his trips to the Balkan states he soaked up musical influences which would emerge in subsequent projects and would have a major impact on the sound of contemporary Irish music, even including (via Bill Whelan) the original Riverdance score.
When he returned to Dublin, Sweeney's Men was breaking up, and the music scene had changed. He met Dónal Lunny, and played with him for a while, but he got his big break when Christy Moore, an established musician in the British folk music scene, decided to record his second album in Ireland. Among the musicians he asked to perform with him were Irvine, Lunny, and uilleann piper Liam O'Flynn. The album, Prosperous, was released as an album by Moore, but the four musicians thereafter formed Planxty.
The group was an instant success, signing a six-record contract and touring throughout Europe. They played mostly traditional songs and tunes, but several were Irvine compositions, making him the lone composer of the band. Instrumentally the group was notable for the intricate bouzouki and mandolin counterpoint of Lunny and Irvine, along with O'Flynn's exceptional piping; Irvine and Moore (who also played guitar) were the principal vocalists. After two albums Lunny left the group, and was replaced by Moynihan. After a third album together Moore departed and was replaced by Strabane native, Paul Brady, but soon Planxty broke up, substantially in debt.
Irvine continued to play with Brady, recording an album together (Andy Irvine and Paul Brady) and briefly with De Dannan, but he soon left due to scheduling conflicts. But by 1978 Christy Moore was ready to reform the original Planxty lineup, complete with Lunny, who brought along flutist Matt Molloy from The Bothy Band. Planxty again broke up in 1982, and Irvine gathered a collection of musicians from throughout Europe and formed Mozaik, who were short-lived.
In 1985 Irvine joined up with fiddler Kevin Burke, guitarist/vocalist Gerry O'Beirne, and accordionist Jackie Daly. Originally billed on an American tour as "The Legends of Irish Music", they soon chose to call themselves Patrick Street. The lineup for the band underwent several changes, but always included Irvine, Burke, and Daly. Agreed to as a "part time" band, they have nevertheless recorded seven studio albums together. Afterwards Irvine partnered with Davy Spillane to record EastWind a collection of various Balkan tunes played Irish-style.
In recent years Irvine has been active in at least four ongoing musical projects: as a solo artist; with Patrick Street; in the original four-man lineup of Planxty, which reunited for several shows in 2003 and 2004; and in a multicultural group called Mozaik (not to be confused with his earlier, similarly-named group), which features Irvine, Dónal Lunny, Bruce Molsky, Nikola Parov, and Rens van der Zalm.
For the last few years Andy has been residing in Letterbreen, Fermanagh, which he recently described as home in an interview with RTE; but he stated that he has a flat in Dublin also.
He is a member of the Industrial Workers of the World (Wobblies).
Like other artists contracted to perform at Féile Iorrais (a community festival in Erris) in August 2007, Irvine was disgusted to learn that Royal Dutch Shell were partly sponsoring the events. Shell's plans for the Corrib gas project have caused serious division and hurt in County Mayo. Irvine donated part of his fee to the Shell to Sea campaign.
In June 2012, Irvine's 70th birthday was celebrated at Dublin's Vicar Street in a pair of concerts in which he was joined onstage by Paul Brady and various members of Sweeney's Men, Planxty, and Mozaik. He has recently been performing in a quartet named LAPD for the first initials of its members, Liam O'Flynn, Andy Irvine, Paddy Glackin, and Dónal Lunny.