O'Hanlon was released by the Scottish Premier League side in August and the 30-year-old has been training with the Cumbrians since December.
Boss Greg Abbott told the club's official website: "We invited Sean along just before Christmas and he has enjoyed himself with us.
"He knows some of the lads anyway and he has fitted in well. We've seen a lot of him and we're delighted that we've been able to bring him in.
"He's a big, strong player who has a lot of experience and games under his belt. We're really looking forward to working with him."
O'Hanlon began his career at Everton but made a permanent switch to Swindon, following a successful loan spell at the County Ground, when he was released by the Toffees in 2004. He played over 100 games for the Robins before signing for MK Dons in 2006.
A move to Hibernian followed five good years in Milton Keynes and he teamed up with Carlisle at the end of last year having been made a free agent by the Edinburgh-based club.