Mick McCann set up the British War Graves project after visiting graves of service personnel near his home in Wigston, Leicestershire.
Having visited cemeteries in France and Belgium about 70 times, he now has more than 750,000 photographs on a website.
Giving the Points of Light award, Prime Minister Theresa May said Mr McCann should be "very proud".
The site covers all wars for which Commonwealth gravestones were issued.
It includes contributions from other people and covers sites as far away as Malaysia and Hong Kong.
Mr McCann said: "Everyone should try to visit one of these cemeteries, they are so moving.
"Some of the inscriptions - chosen by the family - will bring tears to your eyes and it still gets me now.
"Who can stand at the Menin Gate, or at the Theipval memorial, without feeling that? Seventy thousands names - husbands, sons, fathers."
His wife, Joanna, said the work was surprisingly physically demanding.
"In one go we may do two, three or four thousands pictures.
"I've learnt to stand back from the stones, instead of bending over, because doing that many is hard work on the back."
A man who has taken hundreds of thousands of images of British military graves has received a national award.