The 28-year-old struggled with groin and wrist injuries during the Super 15 season and Northampton were not convinced he could cope with the demands of the Premiership.
Sale invited Shepherd to train with them and on Wednesday announced his signing along with that of outside centre Corne Uys from Newcastle.
Director of Rugby Bryan Redpath said: "Cameron has got great pedigree. We're hoping to get him fully fit, so that he can seize the opportunity to make a big impact for this club."
Uys, 30, returns to the Premiership from relegated Newcastle, who he joined in October last year from the Free State Cheetahs.
Sharks chief executive Steve Diamond said: "We need depth among the backs to meet that challenge of the three major competitions in which we are involved, and Corne will get decent game time through the year."
- Bryan Redpath