The 30-year-old, who was released by AFC Wimbledon earlier this month, signed two days after Constable made the switch to the Skrill South champions.
It brings the pair together for a second time, after they combined to good effect in the United squad which won promotion back to the Football League via the play-offs in 2010.
The Hampshire club are managed by former U’s midfielder Richard Hill, who felt a second big signing in succession showed they meant business next season.
He said: “Like James Constable, Jack is an extremely ambitious lad and, to come and play in the Conference, he needed to be convinced that we’re not going into this league just to tread water.”
Latest United news:
2:00pm Friday 21st November 2014
MICHAEL Appleton is keen to explore further the talent pool on offer in Ireland following the signing of Patrick Hoban.
1:50pm Friday 21st November 2014
Here's our match preview spread for Oxford United v AFC Wimbledon with links to all the stories to explore.
9:20am Friday 21st November 2014
NOT many players would pick Sky Bet League Two over the Champions League, but Patrick Hoban is relishing the prospect of a second crack at playing football in England.
9:10am Friday 21st November 2014
Patrick Hoban has put pen to paper at Oxford United, but will have to watch for six weeks before his debut.
9:00am Friday 21st November 2014
CHEY Dunkley is unfazed about the prospect of battling with three more experienced centre halves to get into the Oxford United side.