Bardsley will officially join the Potters on July 1, when his contract expires, and the 28-year-old has penned a three-year deal with Mark Hughes's side.
The right-back progressed through the ranks at Manchester United but was often sent out on loan during his time at Old Trafford.
He moved to Sunderland in 2008 and went on to make exactly 200 appearances for the club in all competitions.
Bardsley played 34 games for the Black Cats in 2013-14 as Gus Poyet's men avoided relegation from the Premier League.
"I'm really pleased to bring Phil in to the club," Hughes told Stoke's official website.
"He's a player of great Premier League experience who I think will bring added quality to the squad.
"He has plenty of qualities that will improve us and help move the football club forward to where we want to be.
"Phil was genuinely excited to join and I'm delighted to bring him in as his personality and desire will shine in the dressing room."