Officers attending a blaze in a Notting Hill neighbourhood in London came across the former soap star tackling the fire with an extinguisher.
Jason was also pictured wearing just his underwear as he approached the burning building, having spotted the flames from his house across the road.
The fire brigade were called to the incident at 4.09am on Sunday morning, which is believed to have been caused by a fault in electrical cabling.
Officers later confirmed nobody was hurt.
London Fire Brigade Watch Manager, Thomas Wolfe, said: “The fire was located in the side passage next to a house and when we arrived a gentleman was tackling the fire using a fire extinguisher. We took over from him and quickly dealt with the blaze.
“It soon transpired that it was Jason Donovan who noticed the fire from his property over the road.”
Asked if the actor would receive a commendation for his bravery, he quipped: “He looks good for his age. As one of the firefighters said to the resident, ‘everyone needs good neighbours’”.
Jason later tweeted about the incident, joking about his state of undress while helping to tackle the blaze.
He wrote on the social media site: “Thank you to the @LondonFire for getting to the situation so quickly, glad no one was hurt.
“This is a good reason to always wear PJ s to bed ( in case of emergencies ) but much more importantly to have fire extinguishes at hand in the home.”