28-year-old Louis has put pen-to-paper on a one-year contract after weeks of negotiations with Terras player-manager Jason Tindall.
"Jefferson finished last season with Havant & Waterlooville," Weymouth chief executive Gary Calder said.
"Before that he had spells with Yeading and Stevenage Borough and at the start of the 2005-06 campaign he was at Bristol Rovers.
"He has also played for Woking, Forest Green Rovers and Oxford United.
Meanwhile, Tindall has also secured the services of star striker Stuart Beavon and midfielder Danny Phillips on one-year deals.
"There has been a lot of interest in Stuart Beavon and rightly so," Tindall told the Dorset Echo.
"He is a fantastic player and I think anyone who has seen him play will agree with that.
"The fact that he has now signed is fantastic, there have been a lot of teams waiting to pounce."
Tindall was also full of praise for Phillips saying: "I was lucky enough to play with Danny before he came to Weymouth and that is one of the reasons why I was so keen to get him in.
"Ability-wise and talent-wise there is no one better in our league. Some of the things he does in training can make everyone stand with their mouths wide open and if he was 5ft 10in tall he would be playing in the Premiership.
"But I am not concerned about his height. He is a fantastic lad and a very talented player, and to get him in is a credit to the football club."
Source: http://www.confguide.com/newsArticle.do?id=6721