The tighthead prop made his debut for Ulster against Biarritz in 2006. He has played 86 times for Ulster, scoring two tries. His last international cap appearance was against the All Blacks in November.
Commenting on the new contract for the 30-year-old front rower, Ulster's director of rugby David Humphreys said: "Declan is a hugely important member of our squad and has proved at both provincial and international level that he is a top performer.
"His opportunities have been restricted in recent seasons due to injury, so it is great to see him fully fit and playing some of the best rugby of his career. I am delighted that he has committed to Ulster for a further two years."
Stephen Ferris has signed a short-term extension to enable him to continue his rehabilitation from the injury that he sustained against Edinburgh in November 2012.
While the former British & Irish Lions flanker (28) has made great progress, no date has yet been set for his return to action with Ulster.
Humphreys added: "Stephen has shown remarkable drive and determination over the past year as he has worked to overcome the injury that has kept him out for so long.
"We are committed to helping him in every way possible and his new contract extension will mean that he will continue to have the best medical, physiotherapy and strength and conditioning teams around him, to help his recovery."