"We need to build that back up. I am looking forward to pulling on the Ulster jersey again and again as it means so much to me," added the 26-year-old.
Educated at Ballymena Academy and Trinity College Dublin, McCullough was contracted to Ulster Rugby at the beginning of the 2001/02 season.
An all-round sportsman, he represented Ballymena Academy in two Ulster Schools Cup rugby finals, two Ulster Schools Cup cricket finals and two Ulster Schools Cup golf finals.
A mainstay of the Ulster pack, he has represented Ireland at Schools, Under-21 (captain in 2001/02), 'A' and senior level.
McCullough's outstanding performances for Ulster saw him win his first Ireland 'A' cap in March 2005 against France 'A' and he was promoted to the senior squad for the summer tour to Japan where he won his first two full caps.
The lock-cum-flanker came on as a second half substitute in Ireland's 2005 Autumn internationals against New Zealand and Australia and was part of the Ireland 'A' squad that participated in the Churchill Cup in June 2006.