Ambelas, who is survived by his wife and two daughters, was trapped by flames on the 19th floor of the Independence Towers.
He is the first New York City firefighter to die in the line of duty since 2012.
"[Ambelas] was trapped deep into the apartment and he did sustain multiple injuries," said FDNY Commissioner Daniel Nigro. "Ambelas went into the apartment to search for life and did not come out, and by the time his brother firefighters found him, it was too late for him."
The cause of the fire was found to be the electrical cord of an air conditioning unit caught between a bed and a wall.
"We have lost a real hero tonight, and our hearts are heavy," Mayor Bill de Blasio told reporters.
Just two weeks ago, Ambelas was hailed a hero for saving a 7-year-old boy trapped in a roll-up gate.
Mayor de Blasio & FDNY Commissioner Nigro announce the line-of-duty death of Lt. Gordon Ambelas in Brooklyn. pic.twitter.com/nsUUKUBNBp— FDNY (@FDNY) July 6, 2014