The powerful back row forward has made 20 appearances, scoring seven tries, for the Warriors since joining from Cornish Pirates where he made 79 appearances and scored 26 tries.
The New Zealand born player is 6'2" and weighs over 16 stones and now has EQP status through residency.
London Irish Director of Rugby, Brian Smith, is delighted that Blair has penned a three year deal with London Irish saying: "Blair Cowan is in great form at present and he's a player we've been tracking for some time. Blair is a great fit for us, he can play all three back row positions and he's a try scorer. There are a lot of tough players in this league but not a lot tougher than this guy."
Blair Cowan said: "I'm looking forward to moving down South and joining London Irish. There are a lot of great players at the club and a lot of potential to match. I would like to thank Worcester Warriors and wish them all the best for the future."
23 May 13
NOT ONLY are the great and the good of the Aviva Premiership Rugby strutting their stuff at Twickenham today but so are the new generation of rugby players courtesy of the Land Rover Premiership Rugby Cup.
Jonathan McConnell
23 May 13
It was only five games ago that Northampton Saints were steamrolled by their East Midland rivals, but Christian Day insists Leicester Tigers are facing an entirely different team on Saturday.
Jonathan McConnell
23 May 13
Leicester Tigers will rightly start Saturday's Aviva Premiership final as the favourites but Jordan Crane insists the slate has been wiped clean ahead of their East Midlands derby clash with Northampton Saints.
Jonathan McConnell
23 May 13
Worcester Warriors are pleased to announce hooker Chris Brooker will move to Sixways this summer after agreeing a switch from Harlequins.
Jonathan McConnell
12 May 13
A fast start and a gutsy finish ensured Northampton Saints upset table toppers Saracens 27-13 in their play-off clash and secured a spot in the Aviva Premiership Grand Final for the first time in their history.
Charlie Talbot-Smith
11 May 13
A wonderful try from Mathew Tait put the finishing touches to a rampant 33-16 victory for Leicester Tigers, who booked a place in their ninth consecutive Aviva Premiership final at the expense of Harlequins.
Gerard Meagher
04 May 13
Exeter Chiefs ended their Aviva Premiership campaign on a high and secured their place in next season's Heineken Cup in the process with a nailbiting 40-39 victory over Gloucester Rugby at Sandy Park.
Ric Sumner
04 May 13
London Welsh ended their Aviva Premiership campaign on a high with a 33-22 bonus point victory over Worcester Warriors at the Kassam Stadium.
David Jordan
04 May 13
Nick Macleod's late penalty ensured Sale Sharks finished their troublesome Aviva Premiership campaign with a flourish, as they beat London Wasps 21-20 at Salford City Stadium.
Jamie Holt
