Ronald Mitchell, 29, was one of the first firefighters at the scene of the blaze, which broke out on the top floor of a four-story apartment house on Baltic Street in Boerum Hill shortly after midnight.
He was able to hold the fire at bay with an extinguisher and began to crawl through the apartment to see if there was anybody inside.
The apartment was "thick with smoke" and there was very little visibility, a fire official said.
Mitchell made his way into a bedroom where he discovered Slatin Davis, 11, unconscious in bed. He alerted firefighters by radio and passed Slatin to safety through a window.
The boy was taken to the New York Hospital burn center in critical but stable condition, suffering from facial burns and smoke inhalation.
Mitchell suffered a minor cut to his hand.
