The 19th-century French painter Eugène Boudin once described himself to a critic as a “daydreamer who has been content to remain in his part of the world and look at the sky.”

His “part” of the world was the Brittany and Normandy coastline, where he painted splendidly evocative canvases of the fashionable tourists who flocked to the resort beaches at Deauville and Trouville and also captured the quotidian activities of local washerwomen and fishermen.

The sea was a natural subject for Boudin, who as a child had sketched pictures on the steamship his father piloted between Le Havre and Honfleur in Northern France.

There’s something to be said for doing one thing and doing it extremely well — and Boudin, who was quick to acknowledge that he would “always be the painter of beaches,” appears to have reconciled himself to this fate.

With the exception of a handful of countryside sketches, seascapes constitute the vast majority of the 42 paintings, drawings and watercolors that go on display at the National Gallery of Art on Sunday as part of the first U.S. monographic exhibit of Boudin’s work in more than 30 years.

Fellow artist Jean-Baptiste-Camille Corot dubbed Boudin “king of the skies” — and if you’re only looking at the beachgoers, water and boats in the pictures you’ll have missed half his appeal. Take “The Beach at Villerville” (1864), where the gathering of vacationing bourgeoisie serve more to focus the viewer’s attention on the dusky horizon — alternately gray, gold and pink — that subsumes the canvas. Then there’s Boudin’s large masterpiece, “Entrance to the Harbor, Le Havre” (1883), which depicts a roiled, sooty sky hanging heavy over an incoming American ship.

Most of the people in Boudin’s pictures are faceless — which adds an air of anonymity to all, whether rich or poor. Their clothes, however, are marvelously detailed. Some of his watercolors, such as “Four Ladies in Crinolines Walking at Trouville” (1865), could double as the sketches for a fashion designer’s spring line. (Look closely and you’ll even see where the artist penciled in the names of colors he would later add — such as “gris” or gray — to various aspects of the ensembles.) And even peasant girls get their due. “Women on the Beach at Berck” (1881) shows a sextet of young women in white bonnets, some with blue skirts rolled up to reveal what appear to be brilliant red petticoats.

Boudin went to Paris yearly and often exhibited at the Salon there, but he never painted “this devil of a city” as he called it, said the show’s curator, Florence Coman.

Given his nearly single-minded focus, Boudin occupies a unique place in the artistic firmament, Coman said. She noted that he’d been somewhat “marginalized” because he was not a member of either the Barbizon or impressionistic schools, though aspects of each, such as Barbizon’s focus on peasant life, are evident in his work.

And “Yacht Basin at Trouville-Deauville,” which Boudin painted in the mid-1890s toward the end of his career, exhibits a strong impressionistic inclination with its loose, thinly painted brush strokes. It shows a line of boats with multicolored flags flapping from their masts — the flags’ designs glassily reflected in the water below.

Despite his less-than-famous name, Boudin was influential for a number of greats, notably introducing Claude Monet, a founder of Impressionism, to plein air painting. In 1858, Boudin spotted Monet’s caricatures in a Le Havre shop window and recognized “something special,” Coman said. He asked the shop owner to introduce him to the artist (then an unknown), and Boudin subsequently invited Monet to come paint with him on the headlands overlooking the ocean there. Boudin, it seems, was also an excellent matchmaker.

“Eugène Boudin at the National Gallery of Art” is on view at the East Building from March 25 through Aug. 5. For more information, go to www.nga.gov.