The Hammers have bolstered their defense with the signing of the young fullback, seeing off competition from Everton in the process.
Sam Byram has completed his move to West Ham, signing a four-and-a-half-year deal at Upton Park.
The 22-year-old has joined the London club for an undisclosed fee, having reportedly turned down a switch to Premier League rival Everton.
Everton was said to have agreed a 3.7 million pounds ($5.26M) deal to sign the fullback, but he has opted to join Slaven Bilic's side instead.
Bryam, who can play at right back and on the right side of midfield, joined Leeds at the age of 11 and has since gone on to break into the first team and establish himself as a regular in the starting XI.