Pellegrini replaces David Moyes, whose contract was not extended despite steering the Hammers to safety.
West Ham have announced the appointment of Manuel Pellegrini as the club's new manager on a three-year deal, having declined to extend David Moyes' contract this summer.
The former Manchester City boss has been managing in China since leaving the Etihad in 2016, but comes with a stronger reputation than the Hammers' recent history of managers - having won the Premier League with City in 2014 and the Argentine Premier Division twice with San Lorenzo and River Plate.
In a statement on the club's website, co-chairman David 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.
“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.
“We have listened to fans who asked us to be ambitious. We hope they agree it is an exciting appointment. Manuel will shortly announce the names of the new staff he will bring in and he will then get down to shaping the squad he wants. We all wish him the very best of luck.”