Hammell has put pen to paper on a one-year deal following the conclusion of his two-year youth scholarship at Brunton Park.
The 18-year-old came through the club’s academy system to earn three appearances last season. His debut came in the 2-1 home win over Northampton in December and he played the entire second half against Hartlepool at the beginning of this month.
Blues boss Keith Curle said: “Connor has good ability and you can see him having a long career.
“He has a lot of strengths going forward with the ball and that has given him a firm platform to build from. We’ve spoken to him and he knows he now needs to learn the other side of the game very quickly. He has to earn the right to showcase his ability.
“We’re looking forward to working with him because he’s earned his contract. I think he understands the hard work starts here and it’s now over to him to make the most of the opportunity he’s been given.”