The 27-year-old has signed a two-year contract with the Baggies following a stellar Euro2016 campaign with Wales.
Robson-Kanu arrives at The Hawthorns on a free after leaving Reading at the end of last season and was delighted to finally secure his club future.
“It was an important decision for me and my family and we took our time," he told the club's official website.
“But it's a fantastic club and manager and I'm really happy to be here.
“I'm particularly pleased to be back in the Premier League. I am grateful for everything that Reading have done for me and I enjoyed my time there.
“But it's great to take this step."
Robson-Kanu previously played in England's top flight with the Royals, scoring seven goals in 25 appearances in 2012/13.
Delighted to sign for @WBA Its been an amazing summer and looking forward to playing in the @premierleague again! pic.twitter.com/8IxXTaQUCg
— Hal Robson-Kanu (@RobsonKanu) August 31, 2016