Blaney was educated at Terenure College, whose distinguished alumni include Conor O'Shea and Girvan Dempsey, before joining Leinster in 2003.
During his time with his native province, Blaney made 71 appearances - including 16 during their 2007/08 Magners League-winning campaign - and scored five tries.
He has also been capped for Ireland at Schools and 'A' level, and spent last season as strength and conditioning coach with the Terenure College first team, with whom he lined out at hooker in AIB League Division 2.
Commenting on his move to London Irish, the 28-year-old said: "I am delighted to be joining such an exciting team as London Irish next season.
"The club has a great reputation in Ireland and I look forward to following in the footsteps of some of the great Irishmen who have played for the club."
London Irish head coach Toby Booth added: "We are very pleased that Brian will soon be a London Irish player.
"He is a very experienced and tenacious hooker who will complement our current squad perfectly.
"Competition for places is paramount in our squad to sustain levels of performance and Brian will continue our strength and competiveness in the hooker position."
David Blaney, Brian's older brother, is also plying his trade across the Irish Sea. The 31-year-old former Leinster hooker played in Bristol's English Championship final first leg loss to Exeter Chiefs on Wednesday.
Former Ireland Under-21 out-half Gareth Steenson kicked three penalties to give Exeter a 9-6 first leg lead, with fellow Irishmen, Paul McKenzie, team captain Tom Hayes and David Gannon, also part of the Chiefs selection.