Moyes, 56, returns to the Hammers for a second stint after saving them from the drop in the 2017-18 campaign and will face the same task with the team languishing in 17th - a point above the relegation places.

The Scot's first game back in charge will be on Wednesday at home to fellow battlers Bournemouth.

Pellegrini was sacked after Saturday's 2-1 home defeat by Leicester City, their seventh loss in nine games after a promising start to the season.

"It's fabulous to be back," Moyes said in a club statement on Sunday.

"It feels great to be home. I've missed being here ... I enjoyed being around the stadium and I loved being in this part of the world and I missed the club, so I can't wait to get started.

"I think there's got to be a short-term goal for us just now to get the wins to get us away from the wrong end of the league and what we're going to do over the next six months ... "

Moyes was hired by West Ham in November 2017 for six months to replace Slaven Bilic with the east London club in the relegation zone and he led them to a 13th-place finish to ensure their survival in the top flight.

But they did not renew his contract and instead hired Manchester City's former title-winning manager Pellegrini in the close season and he led them to a 10th-place finish last term.

But after winning only twice in the past 14 games, the club, who spent over 150 million pounds ($A280 million) on transfers during Pellegrini's tenure, wanted to make a change quickly to give the new manager time to salvage the season.

"David proved in his short time with the club that he was capable of getting results and we believe that he will start moving the club in the right direction once again," joint-chairman David Sullivan said.

Moyes previously managed Everton, Manchester United and Sunderland in the Premier League.

He also spent a year in Spain coaching La Liga side Real Sociedad between 2014 and 2015.

Australian Associated Press