The 29-year-old made 145 appearances for the Cherry and Whites after joining from Cornish Pirates in 2009.
"I'm extremely grateful to have the opportunity to join London Irish, a club that's very much on the up at present," he said.
Dawidiuk is Irish's 11th summer signing before they return to the Premiership against Harlequins on 2 September.
London Irish have bolstered their front-row options by signing hooker Darren Dawidiuk from Gloucester.