He becomes Baggies head coach Roy Hodgson’s sixth signing of the summer with the fee understood to be an initial £4.5m, rising to a possible £6.5m with add-ons.

Long is currently on international duty with the Republic of Ireland, preparing for tomorrow’s clash with Croatia in Dublin.

But he will be in contention to make his West Brom debut in Sunday’s Barclays Premier League clash with Manchester United at the Hawthorns.

Albion announced the deal after the results of Long’s medical proved positive. He becomes their sixth signing of the close season but the first for whom they have paid a transfer fee.

Billy Jones, Gareth McAuley, Zoltan Gera and Marton Fulop were Bosman transfers while Ben Foster signed on a season-long loan from Birmingham.

Long has been Baggies head coach Roy Hodgson’s number one striker target throughout the summer to provide support for last season’s top scorer, Peter Odemwingie.

He scored 25 goals for the Royals last season and was linked with a move to West Ham.

Reading also confirmed Long’s move in a statement with chairman Sir John Madejski saying: “Shane has been a conscientious and loyal servant for Reading.

“Water will always find its own level, and nobody can deny a talented young player the opportunity to play at the highest level when they have the ability to do so.

“Had we won (the play-off final) at Wembley, I have no doubt that Shane would still be playing for Reading, but we wish him great luck at West Brom.”

Reading manager Brian McDermott said: “West Bromwich Albion and Roy Hodgson are very lucky to get Shane and I’m sure their fans will see what a great talent he is and how hard he’ll work for the team.”