Potter has been out of management since he was fired by Chelsea in 2023 after just seven months in the job at Stamford Bridge. He signed a two-and-a-half-year contract.
"It was important to me that I waited until a job came along that I felt was right for me, and equally that I was the right fit for the club I am joining. That is the feeling I have with West Ham United," he said.
Potter takes over a team that has won only three of its past 11 games and is 14th in the standings, seven points above the relegation zone.
Former Real Madrid and Spain coach Lopetegui paid the price for that poor run when his departure was confirmed on Wednesday.
The West Ham bubbles have burst for Julen Lopetegui, who was sacked by the Premier League club. (AP PHOTO)
He was hired last May to take the club to new heights after previous manager David Moyes ended West Ham's 43-year wait for a major trophy by winning the Europa Conference League in 2023.
The 49-year-old Potter said West Ham had "everything in place to become consistently successful, both on and off the pitch".
"You don't win a European trophy by fluke - there has to be a good bedrock at a football club for that to happen, and the challenge now is to take that on and build the next steps, to develop a team and a club that the supporters can be proud of," he said.
Potter enjoyed an impressive rise after beginning his coaching career at Ostersunds in Sweden in 2011.
He took over at Swansea in 2018 and by 2022 was in charge of Premier League giants Chelsea after a stint at Brighton.
But his reputation took a hit at Chelsea, who were undergoing a turbulent period following the takeover by US owners Todd Boehly and Clearlake Capital. He lasted just six months after a run of just seven wins from 22 league games.
West Ham said Potter was their "unanimous choice".
His first game will be on Friday (Saturday AEDT) at Aston Villa in the third round of the FA Cup.
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