The 26-year-old moved to Northampton from Rotherham Titans in 2013 and has gone on to make 72 appearances, scoring one try.
Denman played his part in the Aviva Premiership and Amlin Challenge Cup double in 2013/14, coming off the bench in the European final against Bath.
But he has found his game time limited of late, with Kieran Brookes and Paul Hill having dominated the tighthead role during recent times.
And Denman will now move on at the conclusion of this campaign, with Gloucester boss David Humphreys delighted to have acquired the player.
“We’re delighted to be bringing someone of Gareth’s experience and quality into our squad for next season,” Humphreys said.
“We have spoken at length about the importance of our set piece, and Gareth knows what it takes to be effective in that area of the game.
“We already have a talented pool of props in the squad, and with Gareth’s addition, plus the arrivals of Fraser Balmain and Val Rapava Ruskin this summer, we’ve ensured that we have some real strength in depth going forward.”