The 31-year-old prop has made more than 60 appearances for the Johannesburg franchise since making his debut four years ago.
Van Rooyen, who started for the Lions in their Super Rugby final defeat to the Crusaders last weekend, has opted to take up a new challenge at The Rec.
"I'm really looking forward to testing myself in the Northern Hemisphere and playing for a club with a great deal of ambition going into the new season." he said.
Bath director of rugby Todd Blackadder said: "We are really pleased to bring someone in of Jacques' calibre in time for the new season.
"He's proven himself in Super Rugby and will bring a great deal to the squad both at the set piece and with ball in hand.
"We have great strength in depth at loosehead with Jacques, Lucas [Noguera] and Nathan [Catt] all competing for the number one shirt after losing Beno [Obano] to injury in May.
"Jacques can also play at tighthead, which adds another option over the course of a busy season of domestic and European rugby."