The victim was stabbed during a dispute on the southbound platform of the Coney Island Stillwell Avenue subway station that started at around 11:20 p.m.
He got into an argument with an unknown man that escalated to the two rolling on the platform.
The suspect pulled a knife and stabbed the victim in the back and thigh.
The victim staggered to a waiting subway train, where he collapsed in a train waiting car.
The suspect may have gotten on the same train car before fleeing to Stillwell Avenue.
The victim was rushed to NYU Langone Hospital Brooklyn, where he was pronounced dead just after midnight.
The suspect was described as a bald man in his 30s, wearing a green shirt and aqua shorts. No arrests have been made.
It was the ninth homicide in the transit system so far this year. Five people had been killed at this point last year
But overall transit crime is down 6.1%, with most categories showing significant declines. Robberies are down 15.9%, felony assault down 4.8% and grand larceny down 2.8%.
Subway service was affected throughout the morning commute, with no N service between Coney Island-Stillwell Av and 86 St., and southbound N trains terminating at 86 St.
ALSO READ | Sam Champion shares his skin cancer treatment journey
Sam Champion reflects on skin cancer journey, prevention methods
----------
* More Brooklyn news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube