Men of the Docks (1912) has been bought for $25.5m to become the first major American painting to be acquired by the gallery.
It was secured in a deal arranged by New York art dealer Rachel Kaminsky, who acted as a special adviser to the gallery in its search for a pre-eminent American painting for its collection.
This is the first painting by Bellows to enter a UK public collection, and was bought from Randolph College in Lynchburg, Virginia, with backing partly from Sir Paul Getty's fund and private anonymous sources, as part of a new, transatlantic academic partnership, the first of its kind between an American college and a UK gallery.
The National Gallery said it was "seeking to represent paintings in the Western European tradition, rather than solely those made by artists working in Western Europe".
"The acquisition of Men of the Docks, a work made in the Western painting tradition at a vital moment of experiment and innovation in the early years of the 20th century, introduces a previously overlooked dimension to our collection," said a spokesman.
The change in direction began in 2009 with the launch of the National Gallery's ongoing collaboration with the Terra Foundation for American Art, which involves bringing historical masterworks from the US to London "through a series of focused exhibitions".
Bellows was the subject of the first of these shows (An American Experiment: George Bellows and the Ashcan Painters, from March-May 2011), which was seen by 98,000 visitors.
Bellows' work was also showcased in the Royal Academy's exhibition George Bellows (1882-1925): Modern American Life, held from March-June last year. Men of the Docks was included in that display among 71 works covering his career from 1905-25.
Men of the Docks, a 3ft 9in x 5ft 3in (1.14 x 1.61m) oil on canvas, the final and largest in a series of Bellows paintings of workers gathered on a frigid winter day on the New York waterfront, is now on display in Room 43 of the National Gallery alongside major Impressionist works including snow scenes and urban vistas by Monet and Pissarro, "thus linking Bellows with his closest European avant-garde antecedents", the gallery said.
National Gallery director Dr Nicholas Penny added: "Bellows has almost always been seen in the context of American painting, but the way he painted owed much to Manet, and his depiction of the violence and victims of New York derived from Goya and earlier Spanish art. He will seem as modern and original as ever in the National Gallery, but our visitors - many of them from North America - will understand him in a different way. We are thrilled to have been able to purchase this painting."