A modest man, Sir Norman Reid was much less known to the public at large than either his predecessor as director of the Tate Gallery, Sir John Rothenstein, or his successor, Sir Alan Bowness. Nevertheless, he probably had a more dramatic effect on the gallery's development than either.

Most obviously — and strikingly — he was the director who introduced postwar Modernism in all its manifestations to the gallery collections, as well as presiding over the gallery's first large physical expansion since it was opened, with the addition of the North-East Quadrant.

Reid's sympathies with modern, and especially abstract, art were formed early. Born in Edinburgh in 1915, the son of a Victoria Street shoemaker, he was spotted for his artistic talent when he was still at Wilson's Grammar School, and always saw his future as being somehow in art.

This did not worry his father too much, as a school friend had become a commercial artist and, expecting Norman to follow the same path, his father had arranged for him to enter a commercial studio when he left school. Consequently his father was horrified when Norman admitted to him that not only had he gone in for an entry examination to Edinburgh School of Art, but had been awarded a scholarship to study there.

At Edinburgh School of Art he met a fellow student, Jean Lindsay Bertram, whom he married in 1941. By that time he had made his own minor mark as a painter, done a degree at Edinburgh University, and been called up at the outbreak of the war.

He served throughout the war, becoming a major in the Argyll and Sutherland Highlanders. Demobbed in 1946 and looking for an art-connected job in civvy street, he applied to the Tate, because an army colleague told him that Rothenstein was desperately understaffed, and to Chelsea College of Art for a teaching position. He was offered both jobs, and decided on the Tate largely because his wife felt this was the right way for him to go.

“Understaffed” was an understatement: when Reid joined the Tate the administrative and curatorial staff consisted of Rothenstein, Reid, two secretaries and a paymaster. Shortly after Reid's arrival, Rothenstein went off for six weeks with a touring Turner show drawn from the Tate's unrivalled collection, leaving the newcomer in sole charge. Reid remembered this as a great boon, giving him time and opportunity to go through the whole collection, familiarising himself with its strengths and weaknesses.

Rothenstein, of course, had tastes formed in an earlier generation, and paid closer attention to the Tate's role as the national gallery of British art than to its other role as the national gallery of modern art. Reid's view from the start was more international, and more sympathetic to the postwar shift of creativity in British painting from representational to abstract.

Rothenstein, consequently, though brilliant at acquiring work to his own taste on minimal budgets, was not always sympathetic to Reid's urging of a more widely based acquisition policy.

Reid became deputy director in 1954 and keeper in 1959, and when Rothenstein retired from the Tate in 1964, after the quarrels and scandals colourfully related in his autobiographical volume Brave Day, Hideous Night, Reid was appointed to succeed him, as an evidently safe hand on the tiller.

Those who expected Reid not to make waves as director were soon disabused. He immediately moved to acquire important works by leading European artists such as Mondrian, Dalí and Brancusi. Through his personal relations with living artists of his own generation, as well as his own known delight in abstract art, he was able to negotiate spectacular donations from Henry Moore, Barbara Hepworth, Ben Nicholson and Naum Gabo, as well as, most striking of all, Mark Rothko's Seagram murals, which were accommodated in their own space, rapidly dubbed “the Chapel”, in the new North-East Quadrant.

Reid retired from the Tate in 1979, after 33 years there. Interviewed some two decades later, he cheerfully admitted that he did not miss it, and felt little interest in most new art. Towards the end of his reign he had had various clashes with his trustees, after concluding a pact that nothing should be purchased if either the director or the trustees were set against it. Some of these clashes clearly rankled, while some were subsequently reconsidered.

After he left, Reid urged his successor, Alan Bowness, to purchase a large metal piece by Frank Stella that

he himself had rejected. When he came up against the rejection

by the majority of the trustees of a piece by Joseph Beuys, a dissenting trustee, Ted Power, immediately presented the Beuys to the Tate as a personal gift.

During Reid's rule the Tate staged a number of epoch-making exhibitions, including an early gallery presentation of Gilbert and George's Living Statues. Undoubtedly Bowness's ensuing period as director was more circumspect, and by the time Nicholas Serota took over and revolutionised the whole gallery by implementing the long-mooted separation of the British and modern collections into separate buildings, Reid was content to watch from the sidelines and keep his opinions, for and against, to himself.

Reid was knighted in 1970, awarded various honorary degrees and orders, and felt particularly pleased to have been involved in founding the Friends of the Tate and with the charity Paintings in Hospitals. He was also happy to see his own paintings hanging without prejudice in the Scottish Gallery of Modern Art.

Reid's wife, Jean, died this year, and he is survived by a son and daughter, the latter married to the abstract painter Robyn Denny.

Sir Norman Reid, painter and a former director of the Tate Gallery, was born on December 27, 1915. He died on December 17, 2007, aged 91