The England international joins the Baggies as a free agent from July 1 after ending his five-year spell at Manchester City.
The 31-year-old won two Premier League titles at the Etihad and takes a wealth of experience with him to the midlands.
Pardew showed an interest in the player last summer but Mike Ashley would not pay the players wages - even though the player agreed to a wage cut.
The Baggies said in a statement that Lescott's deal has the option of a further year.
He becomes the first signing of new head coach Alan Irvine - the Scot who worked closesly with Lescott at Everton.
Lescott had been linked with a move to Hull or Newcastle, but the 26-cap England man has settled on a move to the Black Country - the place where he started his career with West Brom's bitter rivals Wolves.
Lescott left Wolves for Everton and then moved to Manchester City for £22million in 2009. After initially being a regular, he found opportunities harder to come by in the latter stages of his time with the Blues.
He has made 538 career appearances and scored 39 goals.