Crew manager Gary Walker said: “The man had been choking; he had gone very pale and was barely breathing.
“Two off-duty soldiers were giving him CPR and we took over, taking it in turns between the three of us.
“We used the defibrillator and inserted a nasal tube to aid his breathing.”
Air ambulance doctors then arrived and performed a procedure “to remove the patient’s blocked airway of a large piece of steak”, the fire service said.
Mr Walker said: “It was a case of being in the right place at the right time.
“Our normal drill night on Thursday doesn’t start until 7pm, but we were there early to take part in the vigil and show our support for Ukraine.
“The paramedics said our intervention kept him alive. It shows the importance of First Aid training – it is absolutely vital.”