The 28 year-old arrived at Ulster from Worcester Warriors in the summer of 2011 and he has played 71 times for the province so far.
Callum has represented Ireland at U18, U19 and U21 level. He was also part of the Emerging Ireland side that won the IRB Nations Cup in Romania last summer.
His new contract means that he will be at Kingspan Stadium until at least the summer of 2018.
Commenting on his new contract, Callum said: "I have really enjoyed my time at Ulster Rugby so when I was offered the chance to extend my stay at the province I had no hesitation in saying yes.
"We have a talented side, an incredible stadium and unbelievable support. It's a great set-up to be a part of and I am really pleased that I will be at Ulster Rugby for three more years."
Ulster Rugby's team manager, Bryn Cunningham, added:
"Callum is a strong scrummager with an outstanding work rate around the park.
"He is developing into a big-game player and signing him on a long-term contract means that we have continuity in a key position.
"I believe that his best rugby is still ahead of him, therefore I am delighted that he has signed for a further three years."
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