Capped 71 times by England, the two-time Premier League player put pen to paper on a season-long loan deal for the upcoming 2017/18 campaign.
The 30-year-old has made more than 300 appearances in the league, playing a key role in City's Premier League title wins of 2012 and 2014, along with a successful FA Cup campaign in 2011.
Widely recognised as his country's number one shot-stopper since 2010, Hart will add an extra bit of quality to Slaven Bilic's side next season.
Joe Hart cannot wait for Hammers debut
Hart spoke of his excitement at pulling on the Claret and Blue shirt having returned to England's top tier following his loan move to Serie A side Torino.
"It's important for me to play football and get the opportunity to come here and play is absolutely awesome," he told West Ham TV. "To be playing in the Premier League for a big club like West Ham, I'm really looking forward to the season."
"I've always loved the club. I think you'll struggle to find anyone, apart from the direct opposing fans around London, who doesn't love the club. It's got something about it, it's got a lot of history and I've always loved playing agaisnt West Ham."
"We've moved into London Stadium and we've got Slaven in charge who I've spoken to and I've always enjoyed as a manager. He obviously did a good job with Croatia and he's doing a good job here, so to get the opportunity to come here, it wasn't really a hard decision," Hart continued.
Hart could face parent club in pre-season
The goalkeeper could face his parent club during West Ham's pre-season schedule in Iceland on August 4th as he aims to build up his fitness and establish himself as first choice under Bilic.
Desperate for consistent game time, Hart will have his sights set on featuring in the first game of the season against Manchester United just nine days later.
"I'd like to think I've obviously left Manchester City on loan this season, but the club as a whole, especially the supporters, have always been fantastic to me.”
"I'd never change how I feel about that club, as it'll always be a very special club to me. It'll be fun to play against them because I'll be banned when it comes to the actual season, while I'm sure Manchester United will welcome me with open arms if I get the nod," Hart concluded.