For decades, the onion-shaped golden domes of an Orthodox Christian monastery kept watch over this lush valley in Ukraine’s westernmost corner. But last month, a new, unmistakable symbol appeared: M-shaped golden arches, perched atop a pole at the foot of a mountain.

McDonald’s had finally reached Ukraine’s remote, alpine region of Transcarpathia, and the locals could not be happier.

“We come here every day,” said Anna Bilenets, 22, as she polished off a McChicken during a recent lunch break at a bustling McDonald’s in Mukachevo, one of two cities in Transcarpathia where the chain opened this spring. Around her, children tore into Happy Meals with giddy delight and couples reached into boxes of French fries.

Sitting next to a friend, Ms. Bilenets explained how their McDonald’s visits had become “a routine.” First, they go to a gym nearby. Then, they reward themselves with a cheat meal. “Every time we try something different,” she said with a smile.

The much-acclaimed arrival of McDonald’s in Transcarpathia signals an unexpected trend for the iconic American fast-food chain: In wartime Ukraine, business is booming.