The 27-year-old centre or winger has made almost 100 NRL appearances for Sydney Roosters, Gold Coast Titans, St George Illawarra Dragons, North Queensland Cowboys and Cronulla Sharks.
Macdonald has won nine caps for his native Papua New Guinea. He is hoping to play in his World Cup next autumn.
Macdonald said: “I’m super excited to have signed for Leigh Centurions and I can’t wait to get over and play.
“I’ve heard such a lot of good things about the club and the community and all the people I’ve spoken to at the club have been really friendly and welcoming.