The Eagle director made the comments at Cannes, where he presented footage from his upcoming documentary Marley, Screen reports.
Macdonald said: "When I was working on The Last King Of Scotland in Uganda, I remember going into the slums of Kampala and seeing flags with his face on and hearing reggae pumping out.
"Anywhere you go in the world, Marley speaks to people. He still has this political and social resonance."
He added: "People think he was just this guy sitting around smoking spliffs. He did smoke a lot of spliffs, but at the same time he was the most driven and professional person who worked until four in the morning and was a tough taskmaster."
Marley, who popularised reggae and the Rastafarian religious movement, died of cancer in 1981.