Early in 1986, a gallery opened on Charlotte Street in Fitzrovia, London, across from the advertising agency Saatchi & Saatchi. Its 25-year-old owner seemed the picture of a certain kind of Englishman: small, solid, with unruly fair hair and gold-rimmed spectacles. He wore, as such Englishmen do, well-cut tweeds; it being the Thatcher era, there was no surprise to hear him say that he meant to have a million pounds in his pocket by his 30th birthday. Despite appearances to the contrary, the gallerist was neither British nor a yuppie.

Karsten Schubert, who has died of thyroid cancer at the age of 57, was German; and he played an unparalleled part in promoting the group that would come to be known as the Young British Artists (YBAs).

Until setting up on his own, Schubert had been at the Lisson Gallery – an institution which, as he was later to say, “was where British art of the 80s happened”. This was no exaggeration. In the years before Damien Hirst’s 1988 Freeze exhibition, the Lisson was the only London gallery open to the work of young and as yet undiscovered artists.

Sensing the need for another, and convincing the dealer Richard Salmon to back him, Schubert set about filling his stable. His first exhibition was of the sculptor Alison Wilding, whose work he continued to show until his death. It was in 1988, though, that he met the group with which his name would become most closely associated. Through the artist Michael Craig-Martin, Schubert visited the degree show at Goldsmiths College (now Goldsmiths, University of London). That November, three of the art school’s new graduates – Gary Hume, Michael Landy and Ian Davenport – had their first West End exhibition at Karsten Schubert Limited.

This was followed by a series of shows that helped both to put the YBAs on the map and to define their aesthetic. In October 1991 came the event entitled preserve ‘beauty’, in which another young Goldsmiths artist, Anya Gallaccio, filled Schubert’s Charlotte Street window with 800 gerberas, whose rotting red slime slowly oozed down the glass. The following year came Landy’s Closing Down Sale, the artist converting the gallery into a pound shop complete with cheap consumer goods, shopping trolleys and day-glo signs that read “Going Out of Business”.

These last proved unhappily prophetic. In part due to Schubert’s own energy, the market for new art overheated and collapsed. Far from having made a million pounds, he had, by the age of 30, lost it. So, too, had Salmon. The pair parted company in 1993, Schubert reopening his business in smaller premises in nearby Foley Street.

By this time the YBAs he had helped to invent had begun to desert him. Tact was not always Schubert’s strong point: shortly after Landy’s last show, he had sent a letter around the gallery’s artists outlining the need to trim “dead wood”. This resulted in a number of wounded departures. When, in 1993, Schubert criticised Hume’s new work as lacking in abstract rigour, Hume, too, took himself elsewhere. Rachel Whiteread followed suit in 1996, at which point the second gallery closed.

It did so with typical éclat. The year before, Schubert, with the gallerist Thomas Dane and the publisher Charles Asprey, had opened a space called Ridinghouse to the rear of Foley Street. There they showed works such as Jake and Dinos Chapman’s Bring Me the Head of … (1995): a video in which a pair of local prostitutes pleasured themselves with the nose of the mask of an Italian dealer to whom the Chapmans had taken a dislike.

The Ridinghouse name carries on in a publishing house, producing high-end works of art history and criticism, and artists’ monographs. Schubert was perhaps proudest of this. For all his love of Britain and English tailoring – he became a British citizen not long before his death – he had a depth of culture and historical understanding that remained admirably German.

Born in Berlin, to Ruth (nee Herberer) and Gottfried Schubert, Karsten was educated at a classical Gymnasium at Helmstedt in Lower Saxony. (His parents divorced when Karsten was two, his mother remarrying, to Max Stecher, a businessman.) After this he studied theology at the Humboldt University of Berlin, before taking a job with an art dealer in Cologne.

With his mother, a teacher and social worker, the young Karsten had haunted museums. He recalled an early trip to the Pergamon, in what was then East Berlin: “Suddenly a train would rumble past the windows, disconcertingly high and close, its lights momentarily swaying the forest of sculptures, and then silence and darkness again.” When he wrote his own history of museology, The Curator’s Egg (2000), it was with the easy assurance of one who could quote Marcus Aurelius from memory.

It was this same sense of history that had allowed Schubert to spot what was happening in British art before most British gallerists did. “The classic pattern had been that you were watched by dealers for a while and got an occasional studio visit and pat on the back,” he said of the YBAs. “These artists were not willing to play the game that way. They wanted to change the rules and take the initiative.”

It was an outsider’s eye, too, that enabled him to see British art in an international, rather than a local, context. In between giving exhibitions to artists such as Landy and Hume, Schubert would show Americans such as Ed Ruscha and Germans such as Gerhard Richter. This lent the YBAs an international exposure – and status – that a previous generation of British artists had lacked.

It is the fate of pioneers often to be sidelined by history. Although Schubert did more than any London gallerist to bring the YBAs to fame, it was the next generation of dealers who made money out of them and were credited with their discovery. From the mid-1990s on, Schubert concentrated on artists the rigour of whose art he particularly liked, most famously Bridget Riley. Having her work shown alongside that of artists 30 years her junior re-energised Riley’s late career. Schubert’s last gallery, in Lexington Street, Soho, favoured artists with a strong formal sense, Tess Jaray notable among them.

Schubert’s taste was perhaps best shown by his own collection. In his flat in north London were drawings by Cézanne and Mondrian, hung side by side with works by Jaray and Picasso and a Roman bust bought from the estate of the critic David Sylvester. Its bookshelves were lined with Proust, for whom he had an almost obsessional fondness. When he found a book he admired, Schubert would buy 20 copies of it and send them to people he liked.

This generosity was repaid. Diagnosed with cancer in 2015, he recuperated from treatment at Claridge’s, his hotel bills paid by two friends. The experience was recorded by Schubert in a novel, Room 225-6, the proceeds of which help fund a charity doing research into robotic surgery.

He is survived by his two half-sisters, Anja Kirstein and Clarissa Stecher.

• Karsten Andreas Schubert, art dealer and gallerist, born 12 August 1961; died 30 July 2019