A strong scrummaging front row, 25-year-old Lahiff returns to the Aviva Premiership having experienced Super Rugby with the Melbourne Rebels.
Known for his physically imposing style of play, he previously made over 60 appearances for London Irish.
"I'm really excited to be joining Bath," Lahiff said. "They're a hugely talented, ambitious club, and I know that it is a great opportunity for me to keep developing as a player. I'm looking forward to working with Neal Hatley and the rest of the forwards and pushing for a place in an exceptionally talented pack."
First Team Coach Neal Hatley added: "Max is a very talented young prop, and it's exciting to have him joining us. He is technically really good, and offers a lot around the field as well, and he'll really fit in with the style we are striving to play here at Bath."
Lahiff is set to play a part in Bath's LV= Cup match against Harlequins at the Stoop tomorrow at 14.40.