The 24 year old Welshman joins the London club from Newport Dragons, where he was on loan from Bath.
A strong running centre, Cheeseman previously spent six seasons with the Westcountry side, making 83 appearances. He was capped by Wales at Under-19s level.
Director of Rugby, Conor O’Shea, says:
“With every squad being so stretched at this point in the season, we are delighted to be able to add a player of Tom’s calibre to the squad. Despite his years, he has a huge amount of experience, which will be extremely valuable as we push on to the end of the season.”
Tom Cheesman, says:
“I am thrilled to be joining Harlequins. They are an exciting, young and ambitious team who throw the ball round and play attractive rugby. This is not only exciting for the crowd but is also the kind of rugby that I like to play.
"I am especially looking forward to making my reunion with former Bath player and team mate, Chris Brooker.
"After meeting Conor O’Shea and Mark Mapletoft to discuss the move to Quins, the decision was very easy and I am looking forward to working with them and the other coaches."