John Harley was born in Glasgow.
In 1906 he moved to Argentina (he was a railway engineer) and played for Club Atlético del Ferrocarril Oeste de Buenos Aires. Following a friendly between the two clubs in 1908, he crossed the River Plate to C.U.R.C.C.(Peñarol) for whom he played until 1920.
'El Yoni' made 17 appearances for Uruguay between 1909-1916 , including 7 as player/coach. He is credited with bringing the 'Scottish' passing approach to Uruguayan football.