McManaman has agreed a three-and-a-half-year contract and will cost Albion between ??4m and ??5m if the transfer from Wigan goes through.
The 23-year-old, who has made more than 100 appearances for Wigan, has also been linked with Hull City this month.
But Tony Pulis has won the race for an England U21 international he hopes will bring width and pace to West Brom’s attacking play.
Speaking after last week’s draw at Everton, the Albion manager said: “There are certain areas on the pitch within the group that we have to get to enable us to be better. We do need a bit of pace out wide, without a question of doubt.”
McManaman’s likely exit follows Shaun Maloney’s departure for MLS side Chicago Fire at the weekend.