Four fire engines and around 25 firefighters were called to a flat fire on Hale Lane in Mill Hill.
Part of a four-roomed flat on the second floor of the building was damaged by fire. Firefighters led a man to safety via an internal staircase who was treated on scene by London Ambulance Service crews.
The Brigade's 999 Control Officers took 10 calls to the blaze.
The Brigade was called at 1352 and the fire was under control by 1509. Fire crews from Stanmore, Hornsey, West Hampstead and Harrow fire stations attended the scene.
The cause of the fire is under investigation.