The 26-year-old centre joins from Bristol, where he has just finished his second spell with his home-town outfit. Eves, who played for England in the 2009 World Rugby Under-20 Championships final, has also spent two years at Newcastle Falcons in his career.
Director of rugby Jim Mallinder says that Eves will add to the depth in an important area of the squad.
“With a number of players away with their countries for the World Cup we felt we needed some more depth in the squad,” he said. “Luke is a good player who has plenty of experience in the Aviva Premiership and in the Championship, and we believe he has the quality to be able to contribute as our season gets underway.”