The American actor won the accolade for his portrayal in new flick Manchester by the Sea, which tells the story of an uncle asked to take care of his teenage nephew when the boy's father dies.

He was presented the award by his Gone Baby Gone co-star Amy Ryan, who praised the actor for being "mesmerising".

"That's the nicest thing anyone's ever said about me," Casey said, "Including my mother."

While Casey may have been in a room filled with the biggest names in movie making, the 41-year-old didn't hold back when poking fun at the nature of Hollywood.

"I like to read reviews," he explained. "(Especially when they are) informed without being esoteric, critical without being snarky or personal."

He then proceeded to pull a piece of paper out, and noted New York film critic and NYFCC chairman David Edelstein had been gushing in speaking about most of the winners, but not him. Casey then read out some of David's choice words for his performance.

"Affleck, though likable, doesn't have a lot of variety and resorts to chewing gum to give his character through-lines," he shared.

"Affleck's line readings would be too mumbly and mulish even for the glory days of '50s Method (acting) and he might as well be wearing a T-shirt that says 'Shoot Me.'"

Others lines include, "Fortunately, he's not the lead," and "It's looking like whenever I see Affleck's name in a movie's credits, you can expect a standard, genre B picture -slowed down and tarted up."

The review hasn't dented Casey's awards season chances though, and he has already received nods from the Golden Globes and Screen Actors Guild Awards.

The NYFCC winners were announced on 1 December (16), with the ceremony held a month later.

Other big winners include Casey's Manchester by the Sea co-star Michelle Williams, who took home the Best Supporting Actress prize and Moonlight filmmaker Barry Jenkins, who went home with the Best Director gong.

Best Actress went to Isabelle Huppert for Elle, Best Supporting Actor was Moonlight's Mahershala Ali, Best Film was awarded to La La Land and Zootopia bagged Best Animated Film.