On 7 July 2011, Cork signed for newly promoted Championship club Southampton, after they agreed an undisclosed fee with Chelsea.
Cork ended the 2011–12 season as the only Southampton player who appeared in every league match, as the club earned promotion to the Premier League as runners-up in the Championship.

Cork missed Southampton's opening fixtures of the 2012–13 Premier League, due to an ankle injury, sustained against Bristol City in a friendly and a League Cup victory over Sheffield Wednesday.
On 26 August 2014, he scored his first goal for Southampton in a 2–0 away victory over Millwall in the second round of the League Cup.

He scored his first league goal for the club in a 4–0 home win over Newcastle United on 13 September 2014 and his second and final league goal for the club came in an 8–0 home win over Sunderland on 18 October.
On 7 July 2011, Cork signed for newly promoted Championship club Southampton, after they agreed an undisclosed fee with Chelsea. Cork ended the 2011–12 season as the only Southampton player who appeared in every league match, as the club earned promotion to the Premier League as runners-up in the Championship.
Cork missed Southampton's opening fixtures of the 2012–13 Premier League, due to an ankle injury, sustained against Bristol City in a friendly and a League Cup victory over Sheffield Wednesday. On 26 August 2014, he scored his first goal for Southampton in a 2–0 away victory over Millwall in the second round of the League Cup.
He scored his first league goal for the club in a 4–0 home win over Newcastle United on 13 September 2014 and his second and final league goal for the club came in an 8–0 home win over Sunderland on 18 October.
Jack Cork