The casting announcement for the TV drama's second season was made Monday by Chris Albrecht, the cable network's president and chief executive officer.
Whitfield is battling non-Hodgkin's lymphoma and left the series after one season to focus on his health.
"Since no one can really replace Andy, we realized that we should instead find an actor who can truly lead 'Spartacus' forward," Albrecht said in a statement. "It was important to us to have Andy endorse the idea of recasting this part, which he did in the same heroic manner that he's dealt with his whole ordeal. And that, coupled with our fortune in finding a young actor with the gladiator credentials and the acting ability of Liam, makes it easier for us to keep this hit franchise going."
McIntyre is known for his work in the Australian TV shows "Neighbours" and "Rush." He also appeared in the HBO mini-series "The Pacific."
Production on "Spartacus: Blood and Sand" is slated to resume this spring.