Sir Norman's last picture show

He is to become a special adviser to the institution where he has organised blockbuster shows for 31 years. The move will give him free rein to work with international museums and galleries as a freelance curator.

But he will remain closely involved in creating new exhibitions at the 239-year-old Piccadilly institution.

Staff will be told today and the search for a replacement starts next month. After so long at the heart of one of London's best-known and most influential art institutions, Sir Norman could prove difficult to replace.

Although teaching and promoting the art of its elected members is at the core of the Academy, it is the giant exhibitions programme Sir Norman spearheaded that funds this - and for which it is best known.

Sir Norman, 63, said: "It's quite a difficult decision. I've taken it after deep consideration and there's a certain sentimental sadness attached to it. It's a little bit scary if you're a bit institutionalised. But the Royal Academy is being very accommodating. I'm going to be special adviser on exhibitions and hopefully curate some without going to the endlessly boring meetings that I'm not very good at because I tend to speak my mind because I'm bored.

He added: "At the risk of sounding vain, people have begun to identify me with this place. It may be objectively, subjectively unhealthy."

Rumours of his departure first surfaced during turbulent times when the RA was run - briefly - by Lawton Fitt, an American banker, four years ago.

More recently there were reports of tensions with Charles Saumarez Smith after he joined as chief executive from the National Gallery last year.

But Dr Saumarez Smith and Sir Norman insist that, despite differences, they are friends. Sources suggested that if Sir Norman has been eased out, it was with his agreement. Dr Saumarez Smith described the move to adviser as a "transition". "We're using him for the things he's very good at - his international connections and ability to think about great shows and produce them," he said.

"It's very unusual to have someone as knowledgeable as Norman across the whole range of art. Lots of people are very committed as curators of contemporary art and have international experience but very few have the knowledge and expertise to run big historical exhibitions."

Sir Norman is involved in planning two shows and there are other plans until at least 2012. Of work elsewhere, he said: "I'm keeping my options open."

His hit shows include explorations of the Aztecs, the Turks and Africa as well as artists from Courbet to Mantegna. He believes exhibitions such as Sensation! which brought highlights of Charles Saatchi's collection of Young British Artists to a wider public, have played a part in art history.

The current show is one of Sir Norman's great triumphs. As co-curator spent three years negotiating with the Russian authorities to lend 120 of their finest 19th and 20th century French and Russian works for it.

When he joined in 1977, there were just half a dozen staff including a librarian called Bubbles. The exhibitions - other than the Summer Show - were funded and organised by a mixture of the Foreign Office, sponsorship from The Times and wealthy connoisseurs such as Sir Kenneth Clark of Civilisation fame.

He said: "I like to think that the Royal Academy has become a big international player on the exhibitions scene."