West Ham announced the news late on Sunday evening, adding that Moyes also wants to recruit Billy McKinlay - now in a caretaker role at Moyes' former club Sunderland, who confirmed the Scot had left the club in a statement on their website.
The first training sessions occurred under the new coaching staff.
Moyes has started to put his backroom team together with former Norwich City assistant Alan Irvine joining, while Billy McKinlay, now at Sunderland in a caretaker capacity, is expected to follow suit.
Pearce, who previously played for West Ham for two years from 1999 to 2001, was named as one of Moyes' assistants last weekend and the 55-year-old has backed the team to turn their fortunes around.More news: Arthur Collins trial: Co-accused cleared over club acid attack
With several Hammers now on global duty, the coaching staff will not get a chance to work with the full squad until later this week.
"The prospect of working in the Premier League, at a great club, and alongside David, meant that it was an opportunity I couldn't resist, and I hope that I can now make a positive contribution".
"The main thing is to enhance the togetherness at the club".More news: Shark hits surfer on NSW Central Coast
"Confidence has been dented and that is part of the task, to get that back on track". West Ham will have to however pay compensation to Espanyol at the end of the season should they wish to recruit him.
"I've been doing one day a week this season at Portsmouth, helping out Kenny Jackett, who is a good friend, and I guess that has probably sparked my excitement again in regards to coaching. I'm really excited by the challenge", he said.
Quique Sánchez Flores has never hidden his desire to return to English football, and it could happen sooner than expected.More news: Rally Protesting Meek Mill's Prison Sentence to Be Held in Philadelphia
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