Nial Hamilton – who had 23 years service – was among firefighters called to deal with a burning car at Deeny Drive in Lurgan’s Kilwilkie estate shortly after 9.30 pm on Monday.
They brought the blaze quickly under control but shortly afterwards, the Mr Hamilton collapsed and was found lying beside the appliance where he was storing breathing apparatus.
The 44-year-old was given first aid at the scene before he rushed to hospital.
On arrival, he was pronounced dead.
The head of NIFRS said he was announcing Mr Hamilton’s death “with deep regret”.
Chief fire officer Chris Kerr added: “Today is an extremely sad day for NIFRS and our wider fire service family as we mourn the sudden and untimely death of our much respected colleague firefighter Nial Hamilton who died while on operational duty last night.
“Our thoughts are very much with Nial’s wife Ruth and their two young sons, Alex and Rory, at this difficult time.”
A post mortem examination is to be carried out to try and determine the cause of his death.
Nial Mr Hamilton joined as a fireman in 1990 when he was aged 21.
As a mark of respect the fire service’s flag was flown at half mast at is HQ in Lisburn, Co Antrim where a minute’s silence was held on Tuesday morning at 11 am.