The 23-year-old FA Cup winner is Tony Pulis’s first signing since he took charge at The Hawthorns earlier this month.
"I’m delighted we’ve got Callum and I believe he will be an exciting addition to our numbers,” Pulis said on the club's website.
“Callum is a player who can improve our options and I am really looking forward to working with him.”
McManaman, whose contract includes an option for an extra 12 months, came through the ranks at Wigan and helped the club lift the FA Cup in 2013 when they stunned Manchester City 1-0 in the final but they also suffered the heartache of relegation.
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"When the chance came to move to West Bromwich Albion and return to the Premier League, I couldn't turn it down," he said.
(Writing by Ken Ferris; Editing by Pritha Sarkar)
