He made his debut for Canterbury in the Air New Zealand Cup in 2007. He was also Campbell Johnstone's understudy before he left for France and Franks assumed the tighthead duties for the Canterbury team. His older brother, Ben Franks is also a prop and plays alongside his brother.
Franks made his debut for the Crusaders in 2009 as a substitute against the Western Force but made his first start in the victory over the Bulls and his stellar performance also secured him an All Black contract. Relatively small in stature, he is known for his great scrummaging technique and mobility around the field. He is also very strong, with the ability to squat 240 kg.
His first start for the All Blacks came against Fiji in the Pacific Nations Cup. He won 45–17. Franks was chosen for the 2009 Tri-Nations tournament in New Zealand's first match against Australia. He went on to play the next two games against South Africa before playing once again against Australia. Franks played the penultimate match against South Africa but missed the final match, with Neemia Tialata playing instead. He then came on as a sub against Wales during an international test in November. A week later he started on the pitch in a win over England and went on to be victorious over France a mere week later.
Franks continued with another international tour. His first game was against Ireland with his brother Ben playing with him. They went on to play Wales twice together. He played once again in the Tri-Nations tournament, starting the first four matches against South Africa and Australia. His brother Ben played the third test against South Africa but he missed out. However he appeared in the final match against Australia winning 23–22. He went on to lose the Halloween test against Australia. He took part in four of New Zealand's November friendlies beating England, Scotland, Ireland and Wales. According to the book, "Cory Jane Winging It, Random Tales from the Right Wing," by Cory Jane and Scott Stevenson, Franks and brother Ben are said to have celebrated the All Blacks Rugby World Cup 2011 victory by squatting the next day 240 kg for 10 Repetitions.