Lee Bowyer passed a medical and completed his free transfer to Newcastle on Tuesday.
The controversial 26-year-old midfielder signed the four-year £30,000-a-week contract he agreed in May.
"Lee Bowyer passed his medical at St James' Park on Monday and has now officially completed his transfer to Newcastle United," said a club spokesman.
Bowyer is expected to link up with the bulk of the United squad when they return for pre-season training on Thursday.
He is Sir Bobby Robson's first capture of the summer as the 70-year-old looks to build a squad capable of competing for silverware next season.
Bowyer will be hoping to resurrect his career on Tyneside after his off-the-field problems left a huge question-mark over his international future.
He ended last season at West Ham after joining on a short-term contract in January from Leeds for a knockdown £100,000.
The Magpies have attracted a certain amount of criticism for making a move for Bowyer, following his court case following an attack on an Asian student.
Bowyer was cleared, but his behaviour both on and off the pitch over the years has won him few fans.
Both Robson and chairman Freddy Shepherd have expressed their confidence that a player of undoubted ability can shed the bad-boy image which has plagued him so far.
But he could also prove to be a bargain buy as while at Leeds Bowyer was a much sought-after player, made his England debut and was the subject of a £9m move to Liverpool.
The breakdown of his relationship with the hierarchy at Leeds following his much-publicised court case made his position there untenable.
He was handed a way out of Elland Road by West Ham at the end of last season, but injury and a loss of form meant he made little impact at Upton Park.