The former Hammers midfielder replaces Nuno Espírito Santo, who was dismissed on Tuesday following a disappointing start to the Championship campaign. Parker will take charge for the first time when West Ham travel to Cardiff City on Wednesday.
The 46-year-old arrives with a strong record of winning promotion from the second tier, having guided Fulham, Bournemouth and Burnley into the Premier League in 2020, 2022 and 2025 respectively.
West Ham United are currently eighth in the Championship, six points behind leaders Middlesbrough, having won six of their opening 13 league matches. Parker's immediate task is to restore consistency and get the club's promotion campaign back on track.
The appointment is also a return to a club where Parker spent four years as a player, making 129 appearances between 2007 and 2011. He described the opportunity as a particularly meaningful one for himself and his family.
“It is a very proud moment for me to step into this role and return to a club that means so much to me and my family,” he told the club website.
“There was a warmth, a love, a feeling that I probably didn't have anywhere else. There was something which stood out constantly and that was the relationship that I built up with the fanbase here. That rapport and respect, that I felt instantly.”
Parker said he felt privileged to lead West Ham at a time when the club are seeking an immediate return to the top flight.
“More than anything, this is an opportunity that I am very excited about. I feel privileged and honoured to be the guy that wants to lead us back to the Premier League and be the head coach of this football club at this moment in time,” he added.
He is confident the club share his ambition, having discussed their plans with interim chief executive Karim Virani and major shareholder Daniel Křetínský.
“From my first calls with Karim and Daniel, it was clear they have a shared vision and desire to return the club to the Premier League as quickly as possible. I share that ambition and I'm very confident we can achieve it,” Parker said.
The new head coach will be assisted by first-team coaches Steve Potts, Gerard Prenderville and Billy Lepine, while sporting director Mark Noble will work closely with his former team-mate.
Noble, who made 550 appearances for West Ham as a player, is expected to have an important role as Parker settles into the job. The club have yet to confirm the permanent structure of the wider backroom staff.
Parker is under no illusions about the challenge ahead, but believes his previous experience of navigating the Championship will be valuable.
“I've been in this division three times and I've got out of this division three times. This is a tough division, there is absolutely no denying it,” he said.
“I will use every ounce of my experience, every ounce of my knowledge, to have an understanding of what we're going to need to bring consistency.”
Parker also made clear the enthusiasm he feels about returning to management, saying his energy and desire to take on the role were immediate once the possibility emerged.