Four fire engines and around 25 firefighters tackled a fire on Elthorne Road in Archway.
Half of a flat on the first floor of a four-storey retirement block was damaged by fire. A man was taken to hospital by London Ambulance Service crews. A woman was assessed at the scene for smoke inhalation
The Brigade was called at 0255 and the fire was extinguished by 0422. Crews from Holloway, Kentish Town and Hornsey fire stations attended the scene.
The fire is being treated as accidental and is believed to have been caused by an electrical fault in a cooker.