Fire officials identified the fireman as 42-year-old Gabriel Lee of Ladder Company 12.
In a tweet by the Philadelphia Fire Department, a photo of Firefighter Lee's gear next to his locker is captioned: "A great firefighter who always gave his all & a great friend who always had your back. #DedicationAndService"
Firefighters embraced outside the West Cambria Street firehouse in North Philadelphia Sunday morning.
Black bunting is draped across the front of the building where Lee was found Saturday evening.
Officials say Lee responded to a fire earlier in the day, and had returned to the firehouse to work the night shift.
At some point, fellow firefighters found him unresponsive in the gym in the basement of the firehouse.
He was taken to Temple University Hospital where he was pronounced dead.
Police assembled Saturday night at Temple to escort Lee's body to the medical examiner's office in University City.
Firefighters from a sister station were also on the scene to offer a salute to the fallen firefighter as his body was brought by.
The circumstances surrounding Lee's death are still unclear.
Police and fire officials have not said how he died, but did say more information will be released at the conclusion of their investigation.