Remarking that he disliked racing — unlike his father, who was famous for his palaces and horses — Prince Sadruddin Aga Khan chose a career in politics, that was to see him rise almost to the top of the United Nations, and to devote much of his life to global environmental causes.

Born in 1933, he was the second son of the late Sir Sultan Mahomed Shah Aga Khan, the 48th hereditary Imam of the Ismaili Shia Muslims, and the late Princess Andrée Aga Khan. He was also the uncle of Karim Aga Khan IV, the current Imam.

He was educated in Lausanne and graduated Phi Beta Kappa from Harvard in 1957. After three years of postgraduate research at the Harvard Centre for Middle Eastern Studies, he was recruited by Unesco. In 1961, as executive secretary to its committee for the preservation of Nubia, he directed efforts to raise funds for the great Nubian monuments, including Abu Simbel and the temples of Philae and Kalabasha, which were threatened by the construction of the Aswan Dam.

In 1962 he was appointed the UN’s Deputy High Commissioner for Refugees. By 1965, he was head of the commission, overseeing refugee crises in Uganda (1972), Sudan (1973), Chile (1973), Cyprus (1974) and elsewhere.

Bangladesh’s declaration of independence in 1971 provoked brutal Pakistani reprisals and created a flood of refugees into India. Sadruddin visited the camps and border areas. His answer to Indian accusation that he was a stooge for Pakistan, with whom his family had close associations, was explicit: “I am not pro-Pakistani. I am not pro-Indian. I am pro-refugee.” And his words carried considerable weight: by February 1972, more than seven million refugees had returned to Bangladesh.

From 1978, in the role of chargé de mission to Kurt Waldheim, then UN Secretary-General, Sadruddin directed the efforts of UN agencies, governments and charities. The complexity of his background — as an Iranian brought up in Switzerland in the Muslim faith by an Iranian father and a French mother, and then educated at Harvard — meant that he was eminently suited to his role as an interpreter between East and West.

Despite working intensively and effectively in the role, however, Sadruddin was twice passed over for the post of Secretary-General, once in 1981, and again in 1991. Though he won the 1981 vote, his election was vetoed by the Soviet Union, which considered him too Western. Instead, the post went to the Peruvian Javier Pérez de Cuéllar, under whom, during the late 1980s, Sadruddin co-ordinated efforts to bring aid to the people of Afghanistan.

In the wake of the first Gulf War he negotiated with Saddam Hussein to try to ensure the presence of a UN guard force and the implementation of humanitarian initiatives in Iraq to assist the Kurds and Shia Muslims. He also encouraged Saddam to accept the conditions of the UN’s Oil-for-Food programme. Later, concerned for the welfare of the Iraqi people, he advised that the sanctions should be suspended.

In 1991, Boutros Boutros Ghali was named Secretary-General. Once again, it was thought that Sadruddin was too Western-orientated, and the reputation of his aristocratic family counted against him. Moreover, the United States and Britain disagreed with his belief in a policy of boosting aid to Iraq. Sadruddin made few enemies, though, and was popular among his colleagues. From 1992 until his death, he continued to work at the UN, as chargé de mission to Kofi Annan.

Through his London-based Aga Khan Foundation and private Geneva-based Bellerive Foundation (established in 1977 to promote conservation of natural resources and the protection of all life forms), Sadruddin published articles on humanitarian and ecological issues. He was vocal on numerous subjects, ranging from the plight of monk seals on the Sporadean island of Alonissos to nuclear disarmament, and from the spectacle of a wretched panda trained to play a trumpet in a circus to the detrimental impact on the planet of mass deforestation.

Latterly, however, Sadruddin had become disillusioned with the environmental movement. Before last year’s UN summit on sustainable development in Johannesburg, he argued that the once honourable notion of “sustainable development” was now misleading and was being commercially abused. Multinational corporations and Western-based businesses, he claimed, were engaged in public relations exercises, using a green cloak to cover their continued abuse of the natural world and the exploitation of impoverished populations.

His own approach to the environment was a holistic one. “If you don’t protect the forest, then you can’t protect the wildlife,” he wrote. “If you don’t protect the wildlife, then you can’t protect people.”

Through Alp Action, he endeavoured to halt the progressive urbanisation that threatens the forests of the Alps by emulating the system of national parks in the Canadian Rockies.

The 17th-century Château de Bellerive on the shores of Lake Geneva was not only his home and the headquarters of his non-governmental organisation, but also contained his extensive art collection. Sadruddin’s father had inherited a library of Persian texts, and in the 1950s a folio from the 14th-century Mameluke Koran became Sadruddin’s own first acquisition.

The collection he amassed over the next 45 years included Islamic paintings, drawings and manuscripts from Turkey, Iran and India, and in 1998, 140 items from it were displayed at the British Museum and internationally.

Sadruddin accumulated various honours during his lifetime, including Commandeur de la Légion d’Honneur (France), the Pontifical Order of St Sylvestre (Holy See) and the Order of the Star of the Nile. Last year he was appointed KBE.

Sadruddin’s first marriage, in 1957, to the model Nina Dyer, was dissolved in 1962. In 1972 he married Catherine Aleya Sursock, a Greek born in Alexandria, who survives him.

Prince Sadruddin Aga Khan, KBE, environmentalist and UN executive, was born on January 17, 1933. He died of cancer on May 12, 2003, aged 70.