The midfielder made his senior debut against Derby County on the final day of last season and also completed a brief appearance as a substitute in the Carling Cup defeat to Portsmouth in August.
Delph has been largely restricted to reserve team duty this term, but his maiden professional deal has strengthened the pool of contracted youngsters in Dennis Wise's squad.
Striker Tom Elliott signed senior forms in August, while Jonny Howson, Rob Bayly, Ben Parker and Scott Gardner all received new deals from Wise at the beginning of October.
Delph was part of the pre-season party which travelled to Germany and the Czech Republic before the start of the League One campaign, and he said: "My hopes were to get a pro contract. I've been playing regularly in the reserves, and hopefully I can push on towards the first team. Going out on loan, maybe at the start of next season, would help get me more experience."