Six fire engines and thirty five firefighters and officers were called to a terraced house by passers-by, after seeing smoke coming from the building on Prince of Wales Road in Chalk Farm last night.
The first and second floor of the house was gutted by fire. Half of the ground floor was also damaged in the blaze.
One man was treated at the scene by London Ambulance Service for smoke inhalation.
Fire crews from Kentish Town, West Hampstead, Hornsey, Holloway were at the scene. The Brigade was called at 2239 and the incident was over by 0013.
The cause of the fire is under investigation by the Brigade's fire investigation team and the Metropolitan Police.