The 31-year-old, who has made 26 appearances for the Three Lions, will be out of contract next month after choosing to leave Manchester City, having won the Premier League and FA Cup during five years at Eastlands.
Lescott had been a target of Hull City and Stoke City, as well as Turkish giants Galatasaray, but decided on a move to Albion on Thursday as he underwent a medical and agreed a two-year contract.
He becomes new Baggies manager Alan Irvine's first signing, and the former Everton coach is delighted that he has the opportunity to work with someone of Lescott's pedigree again at The Hawthorns.
"I'm delighted we've been able to agree a deal with Joleon," Irvine told reporters. "He's an England international and a proven Premier League player, who has been at the top level for a number of years.
"He's got Premier League and cup medals to his name and has had a fantastic career so far. When we realised he was available and there was a realistic chance of getting him here we started to work very hard on it. Full credit to the board and everyone at the club for getting this done as quickly and effectively as they did.
"I know Joleon and the type of personality and character he is, in addition to knowing what he can do as a player. He's a great professional and he will add to a number of very good professionals who are already in the squad."
Lescott, who started his career in the West Midlands with Albion's rivals Wolverhampton Wanderers, made 160 appearances for City after moving from the Toffees for a fee of £22m in 2006.