Manuel Pellegrini has signed a three-year contract to become West Ham's new manager.
The former Real Madrid and Manchester City boss succeeds David Moyes, having left Chinese Super League club Hebei China Fortune over the weekend.
Joint-chairman David Sullivan hailed Pellegrini's track record of winning the Premier League title with City as crucial to his chances of ushering in a new era of success at the London Stadium.
"I am delighted to welcome Manuel Pellegrini to West Ham United," Sullivan said on the club's website. "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."
Manuel Pellegrini's path to West Ham appears clearer after he was released by Hebei China Fortune.
The 64-year-old former Manchester City boss has been heavily linked with becoming David Moyes' successor at the London Stadium.
And, in a statement on their Weibo account on Saturday, Hebei said: "We have reached an agreement with Manuel Pellegrini that he will no longer serve as team manager.
"Here, the club would like to express its sincere gratitude to Mr Pellegrini for his contributions and we wish him well in his future work life."
Departing Manchester City manager Manuel Pellegrini admits he has regrets over his decision to announce mid-season he was leaving.
The Chilean is in the final few days of his reign at the Etihad Stadium after the club revealed in February he would be replaced by Pep Guardiola.
Pellegrini decided to go public with the revelation he was to leave just minutes before City officially confirmed a new man would take over in the summer but in hindsight he accepts it had a detrimental effect on his players, as he told the Guardian.
At the time City were second, just three points behind Leicester, but they immediately lost three matches in a row in all competitions and eventually finished fourth, 15 adrift of the champions.
After Guardiola said he was coming to England it was my decision (to go public) because all the media was talking about Guardiola here, Guardiola in Arsenal, Guardiola in Manchester United. It was not fair for all managers - when everyone knew he was coming here.
If I ask if I would do that again... I have some doubts. Yes. I am very self-critical about what I do. Always. I don't want to use (this) as an excuse but it was so difficult to work after that - not for me, for the players.
It's impossible to know if it was the right decision but when you see the consequence of losing immediately three games in a row, when you are winning the last five or something....
The most difficult thing in a group is when you break something. Something was broken in that moment.
Manuel Pellegrini has revealed he will not speak to his successor, Pep Guardiola, about the challenges facing the Spaniard next season following his move from Bayern Munich to Manchester City.
The current incumbent leaves the Etihad Stadium club this summer after three years in charge and has all but secured Champions League football for the team next term, with Manchester United needing to win by 19 goals in their final game to leapfrog their rivals.
Pellegrini suggested that Guardiola had enough contacts at the club not to need any further input, while also hinting that he could remain in the Premier League for his next job.
I don't think that we need to speak. He knows perfectly what is this club, he has friends inside here. He is a very important manager in Europe, so I am sure he will have all the information.
This team in the last five seasons always plays Champions League. So I think he will receive a club he deserves, and I am sure that this club will continue improving in the future.
I will now starting thinking about the future, I don't want to decide just in one week. I will see different options. I am fortunate to work in five countries, but the Premier League is the most important in the world.
The stadiums are full capacity, a party every game, fans uniting and singing. The atmosphere. It is important for managers to have this experience.
Manchester City boss Manuel Pellegrini claimed his side were "forced" to field such an under-strength team at Stamford Bridge in the FA Cup on Sunday (City lost 5-1), given the fact they travel to play Dynamo Kiev in the Champions League on Wednesday and are troubled by injury.
"We are forced to do it," he said. "I think that if we play on Saturday it's better for us because we have to play for England in the Champions League."
Manuel Pellegrini is not surprised by the latest changes at former club Real Madrid but says he feels sorry for Rafa Benitez.
Spanish giants Real, notorious for their high coaching turnover, axed Benitez after just seven months in charge and installed Zinedine Zidane as his replacement.
The 62-year-old said of Real: "At least I finished the year! But I knew from the beginning I was not to continue for the next year. There were some important differences with the president.
"I am sorry about Rafa Benitez because I think he is a manager that deserves respect but it is not strange what has happened at Real Madrid in the last five or six years.
"Yes, (it is) absolutely different (at City). It is another way to think about the role of the manager. A lot of things are different.
"That is why one team is changing manager every year, and at this team it is not the policy of the owners to change immediately when you don't win a title. Different projects for each club."
"Always to manage a big team is very difficult, Real Madrid is a very difficult team. But it is more difficult in the way they manage the club than the position of the manager."
Manuel Pellegrini wants his Manchester City team to be in prime position to launch their title charge from February.
City are third in the Barclays Premier League at Christmas, six points behind leaders Leicester and four adrift of second-placed Arsenal.
The Chilean said: "I think it's very important to be involved, as we are now, at the end of January. If you can be leaders before then that is better, but I think you need to be there on the last day of January. Then, in the last three months, you can win the title."
City travel to Leicester on Tuesday for another big clash but must first negotiate Sunderland at the Etihad Stadium on Boxing Day.
Pellegrini said: "We need to focus game by game. The next game is Sunderland and we must try to beat them here. That's never an easy game.
"Only after that do we think about Leicester. It's very important to win these two games to finish off the first round (of fixtures).
"We lost important points against Arsenal. I said before the game that it was a game of six points but it was not a decisive game. I repeat that you never win the title in December."
Manuel Pellegrini was pleased with Manchester City's win over Sunderland after successive defeats to Juventus and West HamRead the full story ›
Manchester City have thrown their Premier League title defence "into the garbage", according to boss Manuel Pellegrini.
City head into Sunday's Manchester derby fourth in the table, nine points off leaders Chelsea, who have a game in hand.
The defending champions were level with José Mourinho's side at the start of 2015, but have since lost to Arsenal, Liverpool, Burnley and Crystal Palace in the league, as well as being eliminated from the FA Cup and the Champions League.
It has not been a good season. It was not so bad until the end of 2014, when we were top of the table and also had the FA Cup and Champions League.
But in the last three months we have thrown it into the garbage.
I think always for the fans it is important to finish as near to the top of the table as you can and that's what we must do.