As Ukrainian troops began to push the Russians back from the outskirts of the city of Kharkiv in May 2022, Gamlet Zinkivskyi, a street artist who knows how to shoot as well as paint, was eager to fight for his hometown.

So Mr. Zinkivskyi, who had frequented firing ranges before the war, joined a volunteer unit defending the city, in Ukraine’s east. But the battalion’s leader had other plans for his skills.

“Gamlet, just pick up your paintbrush, and go paint in the street,” Vsevolod Kozhemiako, the commander of the volunteer Khartiia battalion, recalled telling him. “Because the power of his art is much stronger than him taking a machine gun and assaulting or defending trenches. His art could empower the people defending the city.”

Although skeptical, Mr. Zinkivskyi obliged and began painting in Kharkiv’s bombed-out and deserted streets, wearing a bulletproof vest where he tucked painting tools.

One of his first works, on a plywood panel covering a smashed door at City Hall, featured Molotov cocktails — a nod to the homemade weapons that residents had prepared to defend Kharkiv, Ukraine’s second-largest city.

“Hellish hospitality,” he wrote on the mural.

Soon, he said, volunteers and soldiers would stop by in the streets where he was working and tell him, “Gamlet, we love your work — keep going!”