Pellegrini had been identified as the club’s top target to replace David Moyes, who left the club at the end of the 2017-18 season, ahead of the likes of Newcastle manager Rafael Benitez and Arsenal manager-in-waiting Unai Emery.
The Chilean has signed a three-year contract, and it is understood that he will become one of the highest-paid managers in the Premier League, earning roughly £10 million ($13m) per season.
The club have been keen to appoint a manager with Premier League experience, and sources have confirmed that Pellegrini is set to be given the chance to bring in his own Head of Recruitment as co-chairman David Sullivan throws his full weight behind the ex-Manchester City boss.
Sullivan said: “I am delighted to welcome Manuel Pellegrini to West Ham United. He is one of the world’s most respected football coaches and we look forward to working with him.
“It was important that we appointed someone with knowledge and experience of the Premier League, who already has an understanding – not only of the teams and players we face – but of West Ham United and our ambitions.
— West Ham United (@WestHamUtd) May 22, 2018
“Manuel brings a reputation for attacking football and getting the best out of his players. We believe he will attract new talent to the London Stadium as well as improving the current squad.
“Above all, he is a winner, who knows what it takes to succeed at the highest level and is driven to continue that success. Manuel is the first West Ham United manager to have a Premier League title on his CV, and we believe that his experience, quality and proven record of taking teams forward quickly will ensure that he is successful here.