Lance Corporal Jonathan McKinlay from Darlington was shot through the neck while on patrol with the 1st Battalion The Rifles in Helmand in September last year.
At an inquest in Chester-le-Street, his family heard his injuries were "non-survivable", despite the efforts of comrades.
He was one of 12 British servicemen who were accompanied by Afghan police and an interpreter when they came under fire.
Navy Medic Stuart Freeman, who was attached to The Rifles at the time, said L/Cpl McKinlay was in a field with the police, who had decided to pray.
When he reached him, there were no signs of life.
Pathologist Dr Russell Delaney found the father of three died from a "non-survivable" gunshot to the neck, which would have left him almost instantly unconscious.
Coroner Andrew Tweddle concluded the Darlington soldier was shot by insurgents.