Harlequins have strengthened their front row with the capture of the Saints star on a two-year contract.
The 27-year-old, who made his international debut against Argentina four years ago and has since gone on to play three further times for his country, is looking forward to stepping out for his new club next term.
He said: "I'm delighted to have the opportunity to play at the best club in the Premiership. The team play with smiles on their faces, a sure sign that they enjoy their style of rugby.
"I'm looking forward to being part of that, to improving my game and to working with the coaches and players to contribute to further success for Harlequins."
Harlequins director of rugby, Conor O'Shea, believes Doran-Jones' acquisition can only be good news for the Premiership club.
He said: "We are very fortunate to be able to bring in a player of Paul's ability. He comes from a fabulous club and has been coached by one of the best forwards coaches in the country so I have no doubt he will add greatly to what we have at Harlequins."