Philip C. Jessup Jr., who retired as a top executive of one of the world’s largest nickel mining companies and then commenced a career negotiating the legal framework for acquisitions and exhibitions at the National Gallery of Art, died Aug. 28 at a hospital in New York. He was two days short of his 87th birthday.

The cause was liposarcoma, a rare form of cancer that attacks fat cells, said his wife, art historian Helen Ibbitson Jessup.

Mr. Jessup’s family made distinguished contributions to law, education and medicine. His relatives helped start institutions including the Johns Hopkins School of Hygiene and Public Health and the American University of Beirut.

His father, who taught at Columbia University and was an authority on international law, played a leading diplomat role in brokering the end of the Soviet blockade of West Berlin after World War II, then served as an American representative to the United Nations and a member of the International Court of Justice in The Hague.

The younger Jessup spent much of his career with International Nickel in New York and Toronto. In the late 1960s and 1970s, the company, known as Inco, entrusted him to help create a billion-dollar mining and smelting operation on the Indonesian island of Sulawesi.

Philip C. Jessup Jr. (Courtesy of National Gallery of Art )

In 1977, Mr. Jessup was drawn into the Suharto-era criminal justice system in Indonesia. The New York Times reported that an unstable Jakarta lawyer working for Inco was quietly let go from the company with a large severance package, but the man retaliated by suing Mr. Jessup for criminal libel.

Mr. Jessup spent months consumed by the case and faced the possibility of four years in jail if convicted. Lawyers for Mr. Jessup told the Times that the judge in the case hinted that a $10,000 bribe would sway his decision. Inco used its leverage with high-level political and diplomatic officials to demand a resolution to the matter, and the charges against Mr. Jessup were soon dismissed.

When Mr. Jessup was asked about how he handled the pressures of living in a developing country, he told the Times, “You learn patience and you learn it quickly.”

Philip Caryl Jessup Jr. was born in Utica, N.Y., on Aug. 30, 1926, and was an Army veteran of World War II. He was a 1949 graduate of Yale University and a 1952 graduate of Harvard Law School. He spent his early legal career at the New York firm of Whitman, Ransom and Coulson and was president of the West Brooklyn Independent Democrats, a reformist group battling the Tammany Hall organization.

After retiring in 1984 from Inco as vice president, general counsel and secretary, Mr. Jessup was recruited to the National Gallery of Art.

He spent 16 years as board secretary and general counsel and worked on agreements that involved sensitive matters: government indemnity of artwork valued in the hundreds of millions of dollars; the acquisitions of major gifts and collections; and forging compromises with corporate sponsors and wealthy donors used to having their way regarding displays, catalogues and gallery perks.

Mr. Jessup was a resident of Washington’s Georgetown neighborhood until moving in 2000 to Norfolk, Conn., where his mother’s family had lived for seven generations.

He was a trustee emeritus of the Asia Society in New York and helped develop the society’s Washington branch. His memberships included the Council on Foreign Relations.

His first marriage, to Dorothy Kerr, ended in divorce. Survivors include his wife of 44 years, art historian Helen Ibbitson Jessup of Norfolk; three children from his first marriage, Timothy Jessup of Jakarta and Nancy Jessup and Margaret Jessup, both of Northampton, Mass.; four stepchildren, Genevieve Cook, Lucinda Martindale of Dingle, Ireland, Francesca Cook-Hagen of Brussels and Alexander Cook of Manhattan, N.Y.; and eight grandchildren.