The 64-year-old flew into London for talks after leaving his job with Hebei China Fortune over the weekend.
The ex-Real Madrid manager was in charge of City from 2013-16 and won the 2013/14 Premier League and League Cup double with the Citizens, before being replaced by Pep Guardiola.
Final negotiations were concluded on Monday night. The Chilean succeeds David Moyes, who was released at the end of his contract after guiding the Hammers to a 13th place finish this season.
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.”
The 46-year-old Spaniard is, like the man he is rumoured to be succeeding at the Emirates Arsene Wenger, a football nut.
Former Spain winger Joaquin, who played under Emery at Valencia, told The Guardian of his old boss: “Emery put on so many videos I ran out of popcorn!
“He’s obsessed with football – it’s practically an illness. He’s one of the best managers I’ve had. I worked with him for three years. I couldn’t handle a fourth!”
A near 22-year stint like Wenger’s may be out of the question then, but Arsenal fans would no doubt settle for a short reign were he to replicate some of the success he has had in his managerial career.
As a player, Emery, whose grandfather and father were both footballers, spent most of his career in the Spanish second tier prior to retiring at 32 due to a knee injury.
As a manager, Emery made a greater impact, guiding his first two clubs Lorca and Almeria to promotions prior to landing a job at Valencia.
There were three successive top-three finishes with Los Che before a short-lived, unsuccessful spell at Spartak Moscow. On Emery’s website there are a list of achievements next to each club he has taken charge of. For the Spartak entry, where he spent six months, there is nothing.
At Paris Saint-Germain he would win one Ligue 1 championship and four domestic trophies across a two-year span, but there were also a pair of last-16 Champions League exits.
The most notable came against Barcelona last year when PSG threw away a 4-0 first-leg lead to crash out.
The video of that 6-1 second-leg loss at the Nou Camp would have made for grim viewing, as have some of Arsenal’s later performances of the Wenger era.
Emery posted a message on his Twitter account when Wenger’s departure was confirmed last month – a post which has now taken on greater significance.
He said: “Impossible to talk about @Arsenal, the @premierleague and the profession of coach without mentioning Arsene Wenger, one of the references probably. Thank you Arsene!”
For a man so consumed by video analysis – he claimed he spends “12 hours” watching clips for each game – Wenger’s Gunners will now likely be his reference point over the coming weeks.
And though Emery has European pedigree and an impressive CV, Arsenal fans seem unsure if he can produce a team capable of compiling the highlight reels they want to see.