The prince died on Monday in hospital in Boston in the United States after a long illness, an official of one of his foundations told AFP.
After a career in the United Nations that spanned nearly 40 years, the prince devoted himself to defence and environmental issues.
Born in Paris in January 1933, Prince Sadruddin, whose name means "defender of the faith" in Arabic, was the younger son of Mahomed Shah Aga Khan III.
After studies at Harvard University, the prince began his UN career in 1958, serving as the UN High Commissioner for Refugees (UNHCR) from 1965 to
The present head of the UN refugee agency, Ruud Lubbers, said all in the organisation were deeply saddened.
"He left an indelible print on UNHCR's history -- leading the agency through some of the most challenging moments," Lubbers said: "Sadruddin's name became synonymous with UNHCR."
Prince Sadruddin served during 1990-1991 as personal representative of the then UN secretary general, Javier Perez de Cuellar, for humanitarian assistance during the first Gulf war.
An avid collector of Islamic art, the prince was also a founding publisher of The Paris Review literary journal, and wrote extensively on nuclear disarmament, humanitarian and environmental issues.
Prince Sadruddin served on the boards of several environmental groups, and as a vice president of WWF International.
He was the younger son of Mohammed Shah Aga Khan III and uncle of Karim Aga Khan IV, spiritual leader of the Shiite Muslim Ismaili community which has a following of 15 million faithful, mainly in central Asia and the Middle East.
Of Indian origin with a French mother, Sadruddin Aga Khan belonged to one of the richest families in the world. He married Catherine Aleya Sursock in
His home was Bellerive Castle on the outksirts of Geneva, and he held four passports, those of Iran, Pakistan, France and Britain.
Prince Sadruddin began his working life as a consultant to the United Nations Educational, Scientific and Cultural Organisation (UNESCO) in Paris in
He joined the office of the UN refugee agency the following year, and was appointed UN High Commissioner for Refugees in 1965, aged 32.
Under his aegis it was involved in coping with major refugee major crises in Biafra during the Nigerian civil war in the 1960s, in Bangladesh, Vietnam and in Chile.
Prince Sadruddin won widespread admiraton for his supervision of the massive exodus of refugees from the war in East Pakistan, which was to become Bangladesh.
He led a humanitarian mission in Lebanon in 1978 and three years later became the UN Human Rights Commissioner's special rapporteur on the mass exodus of populations.
In the same year 1981, he applied to become Kurt Waldheim's successor as UN Secretary-general, and actually obtained more votes than the man who got the job, Javier Perez de Cuellar.
But the Soviet Union used its veto as a permanent member of the UN Security Council to block his election to the post.
The present-day UN Refugees High Commissioner, Ruud Lubbers, received the news of Prince Sadruddin's death while on mission in west Africa.
"He was at the helm of the UN refugee agency during one of its most difficult periods," he said: "This included the 1971 the Bangladesh crisis, which uprooted 10 million people, the 1972 exodus of hundreds of thousands of Hutus from Burundi to Tanzania and the Indochinese boat people tragedy of the mid-1970s."
Prince Sadruddin also served in 1988 as UN coordinator for the reconstruction of Afghanistan and two years later became coordinator of humanitarian aid on the Gulf, remaining in the post until December 1991, after the first Gulf war.
In 1977 he set up an environmental protection body, the Bellerive Foundation, and 1989 Alp Action, devoted to protecting the Alpine environment.
The prince also possessed an impressive collection of Islamic art, put together over 50 years, including paintings, drawings, and manuscripts from Turkey, Iran and India, dating from the 14th century.