The 25-year-old midfielder, who spent the final few weeks of the season on-loan with Graham Rix's side, has agreed on a two-year contract at the Kassam Stadium.
"It is a massive boost. He has a lot of ability and really enjoyed it here. He turned down other offers to come to Oxford and I'm delighted," Rix told the Oxford official website.
"He is a key player and will do a good job for us."