The midfielder, formerly of Huddersfield and Scunthorpe, predicts an exciting future for Oxford.
He told the club's official website: "Having spoken to the manager and the chief executive there is something special happening here and I'm excited to be part of it.
"The lads have made me feel welcome and I'm looking forward to it and am excited about what is going to happen here this season."
The former Republic of Ireland international was part of Scunthorpe's League Two promotion-winning side last season and picked Oxford from a host of suitors.
He added: "It was always a case of me looking for the right club because I am ambitious, and Oxford certainly ticks that box for me. Every team at the start of pre-season backs themselves for promotion; even those that have been in relegation fights the year before think it might happen! But I genuinely believe that it can happen here.
"The manager is ambitious and has worked at a higher level, and has that experience which will have helped him.
"Hopefully this club, and myself as a player, can benefit from that. I spoke to him about the plans to move the club forward and I think those will become evident over the coming months.
"It's nice to be part of that now and to be involved in the games. I can't wait for the season to get under way."