Andrew Pano, 90, died at Massachusetts General Hospital, the Boston Fire Department said.
Pano was one of two people fire crews pulled from Saturday's fire that broke out at the three-story building at 265 E St. about 9 p.m. The other victim, an elderly woman who lived on the third floor, is still in serious condition at Brigham and Women's Hospital.
The one-alarm fire started in the man's second-floor apartment and was caused by an electrical short circuit, the fire department said.
A firefighter was also taken to a hospital for treatment of a cut.
Pano is the second person to die in a fire in Boston this year. An 81-year-old woman died after a fire broke out in a Hyde Park home last month.