Brooker, 24, scored two tries in five appearances for Gloucestershire in 2013.
The fomer England Students representative is looking forward to his new challenge.
He said, “From what I have been told there is a good foundation the club is built on and the progression the club makes to make is something to look forward to and I am excited to be a part of it.
“My aims for this season are to improve myself as a player by trying to improve my own ability and I will be working hard to achieve this as we progress through the season.”
Tony Benson, Oxford head coach, had this to say:
“He’s a big powerful centre who trialled last year but didn’t get in.
“However he came back this season and really impressed me. He has trained well in pre-season and I am looking forward to seeing how he goes.”