Bellows was six foot two and good enough at baseball to attract interest from the Cincinnati Reds. He chose painting instead, moved to New York in 1904, and studied under Robert Henri at the New York School of Art. Henri taught that art should engage with the messy reality of American life, not retreat into academic prettiness. Bellows took the instruction further than anyone in the group.

He painted boxing matches at Tom Sharkey's saloon, an illegal club near the Brooklyn waterfront where bare-knuckle fights happened in a back room. Stag at Sharkey's, painted in 1909 when he was twenty-six, shows two fighters locked together under electric light, the crowd surging at the edges of the canvas. The paint is applied with a violence that matches the subject.

He was the youngest artist associated with the Ashcan School and the boldest. While other members painted park benches and tenement laundry lines, Bellows painted excavation sites, shipyards, snow-covered lots, and river swimmers. The compositions are physically large, thickly painted, and arranged with an energy that makes the viewer feel as though the scene is still happening.

He worked as a newspaper sports illustrator to pay the bills, and the events he covered became paintings. In 1923 he was at the Polo Grounds on assignment for the New York Evening Journal when Luis Firpo knocked Jack Dempsey out of the ring and nearly into his lap. The painting he made of the moment reversed the punch to a left hook because the composition worked better that way. Accuracy was less important than impact.

He died of a ruptured appendix in 1925, at forty-two.