He could not keep Fulham up and left by mutual consent in June 2021. Last season he could not keep Burnley up and departed Turf Moor after relegation was confirmed.
West Ham hope Parker, a promotion specialist, can spark a revival after defeats in their past two matches. Issues this season have included starting games slowly, conceding first and conceding too many.
The club has the same aim of success this season that Parker encountered at clubs where promotion was expected. He has players to be effective going forward and is expected to bring structure and clarity.
Parker is highly regarded at the club from his playing years. His managerial career has included three promotions, followed by leaner spells in the Premier League.
He told the club website it was a proud moment to step into the role and return to a club that means so much to him and his family.
The club said Parker has the complete support of everyone at West Ham. From the conversations we have had with him already, we believe he will represent West Ham United and our supporters in a way that we can all be extremely proud of, it said. There was a warmth, a love, a feeling that I probably didn't have anywhere else. That's exactly why I'm here and why I want to be here, Parker said.