“Now that the 20th century is due to be buried,” Robert Rosenblum wrote in ArtForum in 1999, “it’s safe to reconsider the stuff modernist hierarchies sneered at, particularly art that was once immensely popular among the unwashed masses.”

Rosenblum, who taught art history at New York University for most of the past half century, pitched a big tent in the halls of scholarship and in museum galleries, making room for the likes of Norman Rockwell and other despised crowd-pleasers, who, he asserted, “have become as distant as Victorian narrative painting and Gibson girls, which means we can start to look at them for both pure pleasure and more high-minded studies of art and culture”.

Among Rosenblum’s 18 books was Transformations in Late Eighteenth Century Art (1967). In its preface he referred to terms such as Neoclassicism and Romanticism as “semantic straitjackets” and preferred to delve into the “bewildering new variety of emotions, styles, and iconography” that emerged in late 18th-century art.

His definition of Modernism was expansive, and continually revised, as he shrugged off orthodoxy and embraced both abandoned orphans of art history and newcomers from multiple cultures and genres. Abstract Expressionism had sprung not directly from the angular flesh tones of Les Desmoiselles d’Avignon, he believed, but from earlier landscape painting. He dug up evidence of little revolutions and universal themes, simmering in many cultures in earlier centuries, and connected the dots to contemporary movements. He was instrumental, too, in reviving the reputations of neglected artists, such as Caspar David Friedrich and the Danish artist Vilhelm Hammershoi.

An omnivorous appreciator of artists from the unfashionable Rockwell to the fatally hip Jeff Koons and John Currin, Rosenblum extended his curatorial magnanimity, even, to other species. This led to writings such as The Dog in Art from Rococo to Post-Modernism (1988). For some time Rosenblum kept an oversize photograph of his pet dog, Archie, above the fireplace in his Greenwich Village home, where flea market collectibles cohabited with fine art.

Rosenblum was born in 1927 in New York where his father was a dentist. He attended Queens College and earned an MA at Yale in 1950. After taking a PhD at New York University in 1956, he taught at Princeton, the University of Michigan and Yale, then joined NYU’s Institute of Fine Arts in 1967. A decade later he was appointed Henry Ittleson Jr Professor of Modern European Art at NYU. There, he was a popular teacher of undergraduates and graduates, known for lecturing without notes and for mixing high and low culture into the discourse. In 1972 he was Slade Professor of Fine Art at Oxford, and for the past ten years he also served as a curator of 20th-century art at the Guggenheim Museum.

At the latter his exhibition 1900: Art at the Crossroads, a reassessment of artistic crossinfluences at the turn of the century, was an unruly mix of masters such as Degas and Gauguin, and neglected or forgotten artists. Works from the 1900 World Fair in Paris were included, with examples from Asia, Africa and the New World, and he drew attention to affinities between unlike artists by using thematic groupings, such as “Nudes and Bathers”, “The City” and “Interiors” as a framework for such broader subjects as nostalgia, nationalism and psychology. The critics were equivocal. The New York Times noted that such an assembly of bad art might best be found on eBay, but conceded that the “schlock” was balanced with worthy selections.

Rosenblum had said that he wanted to “reshuffle the deck” and look at the period in a fresh light. His unusual approach — of employing unifying themes and a heterogeneous mix of artists, as opposed to linear, chronological groupings of painters — is now familiar in many museum shows today In 2001, after the terrorist attacks in New York, Rosenblum was a curator of Norman Rockwell: Pictures for the American People at the Guggenheim.

Bringing Rockwell to the Upper East Side was a bit like showing Andres Serrano’s Piss Christ in Peoria. Only in the elite art world could the benign Rockwell stir so much fear, loathing and harsh press. Yet his realist works, evoking moral certitude, bathed in flattering, mid-century light, tugged at patriotic heartstrings for some viewers at a time of national vulnerability. Even critics who had long dismissed Rockwell as a mere illustrator, or considered his work a form of sentimental whitewash, were compelled to re-examine his particular gifts. Was not American cultural history — coming of age, going to war, enjoying prosperity — represented in his cinematic renderings? Was he not a kind of American icon, ripe for deconstruction and admiration? Rosenblum told a television interviewer that the pictures were “great to look at even though we had been brainwashed to think that they weren’t”.

Nevertheless, the exhibition portrayed Rockwell in a dubious moral light, as an opponent of civil rights in the South. Kenneth Silver, chairman of the undergraduate art history department at NYU and an admirer of Rosenblum, described his introduction of Rockwell into the Guggenheim as curatorial gate-crashing and an almost Dadaist act of contrariness.

But Rosenblum, in his writings on Rockwell, was more straightforward than his reputation for mischief might suggest. “The sneering, puritanical condescension with which he was once viewed by serious art lovers can swiftly be turned into pleasure,” he wrote. “To enjoy his unique genius, all you have to do is relax.”

The last exhibition Rosenblum curated was Citizens and Kings: Portraits in the Age of Revolution, which opens at the Royal Academy in February.

Rosenblum is survived by his wife, the artist Jane Kaplowitz, whom he married in 1978, and by their son and daughter.

Robert Rosenblum, art historian and author, was born on July 24, 1927. He died from colon cancer on December 6, 2006, aged 79