The 18-year-old central midfielder began his career at Arsenal, captaining their Under-18 side, before joining the Hammers in July 2015.
"George is someone we noticed a few months ago," said manager Jon Whitney.
"We did our homework on him and spoke to West Ham. He's held in high regard, a player who plays beyond his years."
Five of Whitney's six signings have been midfielders since he was officially appointed manager on 1 June.
Bermudian teenager Kacy Milan Butterfield was the first and was followed into Bescot by Peterborough United's Erhun Oztumer, Sheffield United's Florent Cuvelier and Colchester United's Joe Edwards.
Walsall, who reported back for pre-season training on Wednesday, secured their first loan deal from a Premier League when Southampton defender Jason McCarthy signed for the first half of next season.
"West Ham brought George in from Arsenal where he played as a centre half but was moved forward to play as a holding midfielder which is where we see him playing," added Whitney.
"I know he'll go on to be a top player of highest level and we're lucky that West Ham have entrusted us with his development for the next 12 months. Age isn't a factor. If he comes in and is good enough then he will play."
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Walsall have made their sixth summer signing by bringing in teenage midfielder George Dobson on a season-long loan deal from West Ham United.