Peter Tarnoff, a U.S. diplomat who rose to No. 3 in the State Department in the 1990s after years as a behind-the-scenes envoy, including helping to craft a plan to smuggle six State Department employees out of Tehran during the Iran hostage crisis, in a ruse recounted in the film “Argo,” died Nov. 1 in San Francisco. He was 86.

His wife, Mathea Falco, said he died at home of complications from Parkinson’s disease.

Mr. Tarnoff’s career spanned many crises in the Cold War and beyond. He had served at the U.S. Embassy in Saigon during the Vietnam War and, as undersecretary of state for political affairs from 1993 to 1997, he held policy-shaping roles after the collapse of the Soviet Union.

He was often called to help shepherd politically sensitive decisions by the Clinton administration. Among them was tightening an open-door asylum policy for Cubans fleeing the island, a change in 1995 that outraged Cuban Americans and others who considered it a betrayal of American opposition to Fidel Castro’s dictatorial regime.

President Bill Clinton argued that the shift – sending back Cubans interdicted at sea – was necessary to dissuade Cubans from attempting the dangerous crossing to Florida.

Before making the decision, Clinton wanted to gauge reaction from Castro. Mr. Tarnoff was already known by the Cuban leader – making several clandestine trips to the island in the late 1970s on missions sanctioned by President Jimmy Carter. Mr. Tarnoff and Castro once puffed cigars together.

This time, Mr. Tarnoff reached out to a Castro confidant, Cuban diplomat Ricardo Alarcón, for an off-the-books meeting at a bar near the United Nations. Mr. Tarnoff had an offer: As part of efforts to curb the sea crossings, the United States would take more than 20,000 anti-Castro Cubans sheltered at the U.S. base at Guantánamo Bay.

Castro was in favor. He was worried any unrest at Guantánamo could spread across the island. Mr. Tarnoff and Alarcón later met in Toronto to hammer out the accord. Amid the political bickering afterward, Mr. Tarnoff was put on damage control. He swatted down speculation that Washington was moving toward normalizing ties with Cuba.

“Political dialogue would be a recognition – implicit or otherwise – on the part of the United States that we bear some responsibility for the situation in Cuba,” he told reporters, referring to asylum seekers attempting sea journeys. “We do not accept that.”

More than 15 years earlier, in another under-wraps operation, Mr. Tarnoff was part of a storied diplomatic sleight of hand that played out in Tehran.

In 1979, Mr. Tarnoff was a special assistant to Secretary of State Cyrus R. Vance when Iran’s Western-backed shah was toppled in the Islamic revolution. Later that year, the U.S. Embassy in Tehran was stormed by an Iranian mob, and more than 50 hostages were taken. Six State Department employees who had managed to evade the captors eventually found shelter in the residences of the Canadian ambassador and a top aide.

An elaborate scheme was hatched, later dubbed the “Canadian Caper.” The plan called for two CIA operatives to head to Tehran posing as Canadian filmmakers scouting locations for a science-fiction film, “Argo.” The six Americans in hiding would pretend to be part of the crew, using fake Canadian passports.

Mr. Tarnoff acted as the State Department’s liaison with the CIA and Canadian authorities. He never publicly disclosed the full details of his role. (The Oscar-winning 2012 film “Argo” also did not explore Mr. Tarnoff’s part in the operation.)

Government records, however, put Mr. Tarnoff at the center of dealings during the tense weeks of planning. On Jan. 4, 1980, Mr. Tarnoff wrote a memo to Vance that the six Americans would receive Canadian passports with forged entry stamps. The Canadian Embassy in Tehran would close “right before the exfiltration to avoid reprisals,” Mr. Tarnoff wrote.

Mr. Tarnoff effectively sealed himself off from the rest of the State Department. He feared that any leaks could derail everything. Even Henry Precht, head of the Iranian Working Group at the State Department, was kept out of the loop. “I myself didn’t know what they were planning, so I couldn’t have opposed it,” Precht told the Middle East news site Al-Monitor.

On Jan. 27, 1980, the two CIA operatives and the six American diplomats cleared security at Tehran’s Mehrabad International Airport and boarded a Swissair flight for Zurich. (Fifty-two hostages taken at the U.S. Embassy were freed in January 1981, on the day of President Ronald Reagan’s inauguration.)

After the six Americans in the “Argo” operation were safe, they presented Mr. Tarnoff with a gift: some of the maple leaf lapel pins they wore during their escape.

Peter Tarnoff was born in Brooklyn on April 19, 1937. His father was an executive at Macy’s department store, and his mother was a homemaker.

He was 12 when the family moved to Montreal, where he learned to speak French fluently. He graduated in 1958 from Colgate University in Hamilton, N.Y., with a degree in philosophy. Mr. Tarnoff continued philosophy studies at the University of Chicago but joined the diplomatic corps in 1961 before finishing his master’s degree.

He was posted as a political officer in Lagos from 1962 to 1964. His next assignment was Saigon (now Ho Chi Minh City) in what was then South Vietnam. He rose to become aide to Ambassador Henry Cabot Lodge while the U.S.-led war with communist North Vietnam was escalating.

In 1965, a car bomb detonated outside the U.S. Embassy compound in Saigon, killing two U.S. staff members and almost 20 people on the streets. Mr. Tarnoff was among more than 50 people injured, receiving a head injury from flying glass.

During the 1970s, Mr. Tarnoff held diplomatic and State Department research posts in Europe, and served as special assistant to Vance and his successor, Edmund Muskie.

After Reagan’s election in 1980, Mr. Tarnoff accepted a fellowship at the Hoover Institution at Stanford University. He later became executive director of the World Affairs Council of Northern California and, from 1986 to 1993, was president of the New York-based Council on Foreign Relations.

Mr. Tarnoff’s marriage to Danielle Oudinot ended in divorce. In addition to Falco, his wife of 41 years, survivors include their son, Benjamin Tarnoff; and a son from his first marriage, Alexander Tarnoff. Another son from his first marriage, Nicholas Tarnoff, died in 1991.

Until the late 1950s, Mr. Tarnoff expected to become a professor of philosophy. Those plans were upended by a decision to take philosophy seminars in France. To Mr. Tarnoff, the Cold War realities were vividly clear after Moscow’s crackdown on Hungary’s pro-freedom uprisings in 1956.

“I found myself in Europe at a time when human events and political events were quite dramatic,” he told the University of California’s television channel in 2008. “I think if I had not been in Europe at all . . . I might have continued on with philosophy, become a philosophy professor and never thought about the Foreign Service.”