The youngster has trained with Reading, Manchester United, Tottenham and Falkirk.
McDermott, who will turn 16-years-old in May 2009, is currently contracted to Norwegian side Vag.
McDermott said: “The facilities, coaches, and environment at Arsenal have made up my mind. This is all I’ve ever dreamt of.”
The player’s advisor, Jim Solbakken, added: “Arsenal have shown that they are great at developing young players.
“Sean, at the age of 16, will be given a chance to train with their academy. It is a great chance for him.”
