The 25-year old tighthead prop forward joined Leinster from school before moving across to Galway where he spent two years with Connacht, making 50 appearances. He moved back to Leinster in the summer of 2011.
Jamie was drafted into the Leinster Academy as an 18-year-old in 2005 and was capped, provincially and nationally, through the age grades. In 2007, he was a member of the Ireland team that captured the Under-20 Grand Slam.
Leinster followed his progress at Connacht and in June 2011 signed him back to the Irish capital. He played 18 times during 2011/12 and scored his first try for Leinster in a 42-13 win over Ulster.
London Irish Director of Rugby, Brian Smith said: “Jamie Hagan is a future Irish Test player, he’s cut his teeth in the Rabo Direct Pro 12 and is more than ready to launch his Aviva Premiership career. He’s a tough, uncompromising prop coming into his prime and he’ll add more steel to our tight five. Jamie’s rugby talent and Irish heritage make him a perfect fit for the club. I’m genuinely delighted that he’s committed to London Irish for the next three seasons.”
The prop forward, who has made two appearances for the Irish Wolfhounds, said: “I’m looking forward to moving across to England and joining London Irish. They are a team with a rich heritage and proud Irish traditions which will really suit me. I would like to thank Leinster for all they have done for me and wish them well for the future. I look forward to joining London Irish next season and getting stuck in to Premiership rugby.”