The Premiership club said that 31-year-old Van Rooyen will arrive at Bath ahead of the new season.
He started the Super Rugby final in Christchurch two days ago, when the Lions suffered a 37-18 defeat to the Crusaders.
Van Rooyen has made more than 60 appearances for the Johannesburg-based Lions, making his debut four years ago.
He will enhance Bath’s front-row strength and competition for the loosehead position after they lost England hopeful Beno Obano to an injury earlier this year that could see him miss the entire 2018-19 campaign.
The experienced van Rooyen said: “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.”
Bath Rugby director Todd Blackadder told the club’s official website: “We are really pleased to bring someone in of Jacques’ calibre in time for the new season.”
“He has 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.”
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