Eight fire engines and around 60 firefighters were called to a fire at a bar on Newman Street in Fitzrovia.
A bar in the basement of a five-storey building was damaged by the fire. One man left the building before the Brigade arrived. He was taken to hospital suffering smoke inhalation by London Ambulance Service crews.
Station Commander Dean Wilkinson, who was at the scene, said: "The fire was in the basement of a five-storey building.
"Fortunately, there were no customers in the bar when the fire broke out and a member of staff managed to get out.
"Firefighters worked hard to bring the fire under control and limit the damage."
The Brigade was called at 1903 and the fire was under control by 2053. Fire crews from Soho, Euston, Lambeth, Paddington, Dowgate and surrounding fire stations were at the scene.
The fire is believed to have been accidental and the Brigade's Fire Investigation team believe it was caused by an electrical fault in a bottle washer.