Maguire enjoyed a successful spell at West Ham at the back end of last season and the Premier League club have decided to offer him a move to Upton Park.
The 18-year-old has agreed a two-and-a-half year deal at Upton Park with the Hammers having the option of a further year.
Maguire has been attracting the interest of a host of clubs after his displays with Waterford United over the past 12 months and he is regarded as one of the best young prospects to emerge from Ireland in recent years.
The likes of Blackpool, Brighton, Peterborough and Derby have all shown an interest, but West Ham have won the race for the forward's signature.
West Ham are now waiting for the Premier League to ratify the move for the Republic of Ireland Under-19 international as they look to add Maguire to their squad for the second half of the season.