Clough, 26, came through the ranks at St Helens, and has since played at Salford, Leigh and Blackpool, before playing at Oldham last season, where he scored eight tries in 24 appearances.
He said: “This is going to be a really exciting challenge and one I am looking forward too. This is an exciting project and I cannot wait to get started”
“Looking at the squad that we have put together, we can achieve what we want to achieve, there’s a lot of talent here and the experienced players are being joined by some really promising young talent which looks a good mix after seeing everyone on the first testing session.”
A former Blackbrook amateur, Clough made 17 top flight appearances while at Salford, and also spent time on loan at Harlequins.
Oxford coach Tony Benson said: “John is a very experienced player and can play to a high standard for 80 minutes if required, he is good at gaining momentum and picking holes through the defence and can get the pack going forward and can rip the defence apart. John is a very good defender and has an excellent kicking game.”