The 18-year-old England youth international had attracted the attention of several clubs once it became apparent he would not extend his stay with the Hammers however it is Leeds who have won his signature.
Perkins made appearances in the Premier League and Europa League for the London club last season, coming off the bench against the Whites during Leeds’ 3-2 victory at the London Stadium, as well as featuring against GNK Dinamo Zagreb in Europe.
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Son of former Ireland Under-21 international Declan Perkins, Sonny has represented England at several age groups and is currently an Under-18 international.
"Sonny becomes the club’s seventh summer signing, after the arrivals of Brenden Aaronson, Rasmus Kristensen, Marc Roca, Darko Gyabi, Tyler Adams and Luis Sinisterra,” a statement from Leeds United read.
“He will initially link up with the Under-21s side for the forthcoming season.”
Perkins will compete alongside the likes of Mateo Joseph, Amari Miller, Sean McGurk and Max Dean in the Under-21s attack as the club look to bounce back from last season’s Premier League 2 Division 1 relegation with an immediate return.
The former West Ham teen scored ten times in PL2 Div 1 last term and can play in a wider attacking role or through the middle as a more conventional centre-forward.
It is understood the youngster has been training at Thorp Arch prior to his announcement on Tuesday afternoon.
West Ham will be owed a compensation payment as Perkins officially signs as a free agent, however FA rules stipulate that players under the age of 24 moving at the end of their contract will command a fee paid by the purchasing club.