The former Arsenal man has suffered a torrid time with injuries but is the eighth new signing by manager John Gregory and the manager has expressed his delight at getting the deal completed.
Speaking to the club's official website, Gregory said: "We're delighted to get Conor on board. He was highly regarded at Arsenal but then suffered a bad knee injury which affected his progress. I have spoken to (Hull manager) Steve Bruce at length about him and he speaks very highly of Conor.
"He is coming down a level to play for us but he sees it as a move which will progress his career in the right direction. He's very skilful, passes it and keeps possession well and is a threat in the box too.
"He's had a very good football education but like a lot of young English players he struggled to get opportunities at the top clubs. He's going to find out what League One is all about but this is a great opportunity for him to progress his career again."
The former England and Ireland youth international has said that the manager played a crucial role in convincing him to step down to the third tier.
He said: "The manager sold Crawley Town to me very well. He wants to play good football and that is the way I like to play. It's a new squad he's putting together but a very exciting one and I am looking forward to playing my part.
"I had experience of League One last season on loan so I know a bit of what to expect but it's a fresh start and new challenge for me."