Reagan appointed him as ambassador to Czechoslovakia and later asked him to return to Washington in 1983 to work at the National Security Council, with the assignment to develop a negotiating strategy to end the arms race.

His previous tours in Moscow were as vice consul and third secretary (1961–1963), minister counsellor and deputy chief of mission (1974–1978), and chargé d'affaires ad interim (1981).

[5] After he retired from the Foreign Service in 1991, Matlock reentered the academic world, becoming the Kathryn and Shelby Cullom Davis Professor of the Practice of International Diplomacy at Columbia.

After his 1953 appointment to a position as Russian Instructor at Dartmouth College, he supplemented his income by preparing an index[15] to Joseph Stalin's collected works on contract with the State Department.

His most famous case was Lee Harvey Oswald, who applied for a repatriation loan to return to the United States after having previously moved to the Soviet Union.

[16] Indeed, according to the records received by the Warren Commission, in May 1962, Jack Matlock conducted the exit interview which enabled the Oswald family to leave the USSR and return to the USA.

In June 1961, President John F. Kennedy and First Secretary Nikita Khrushchev met in Vienna, and in December the United Nations General Assembly approved a draft joint resolution on principles for negotiating disarmament.

His predecessor as consul,[21] Frank Carlucci, was later to become Secretary of Defense,[22] and his successor, Thomas R. Pickering, was later to become Ambassador to the U.N.[23] Matlock's next assignment was as Deputy Chief of Mission in the capital of Tanzania, Dar es Salaam.

In early 1976, the State Department made public the fact that the Soviet Union had been beaming microwaves at the Moscow Embassy from a nearby building for many years.

During his tenure, he was able to help resolve a major impediment to good relations: the return of 18.4 tons of gold that had been looted by the Nazis in World War II and kept, ever since its recovery by Allied forces, in American and British banks.

[40] On March 23, 1983, President Reagan announced the Strategic Defense Initiative, a ground and space-based weapons system designed to protect from nuclear attack.

[16] Reagan appointed Matlock to the position of special assistant to the president and senior director of European and Soviet affairs in the National Security Council (NSC) in order to develop a negotiating strategy to end the arms race.

[14][41] Earlier in the year, the long-standing containment strategy toward the U.S.S.R. had been modified by Matlock's predecessor Richard Pipes to include bringing internal pressure on the Soviets while conducting negotiations in the mutual interest.

"[44] While the speech was commonly seen as propaganda, Lawrence S. Wittner, professor of history at the State University of New York - Albany says of it that "a number of officials--including its writer, Jack Matlock Jr.--have contended that it was meant to be taken seriously by Soviet leaders.

While charges against Daniloff were dropped, a diplomatic row ensued, leading by the end of October, to the expulsion of 100 Soviets, including 80 suspected intelligence officers.

[17] The June 1990 summit in Washington brought several bilateral agreements, covering chemical weapons, trade, aviation, grain, maritime boundaries, peaceful uses of atomic energy, ocean exploration, student exchanges, and customs cooperation.

It was to no avail; shortly after his July summit with Bush and 8 days after the end of Matlock's term, Gorbachev was briefly removed from power by the August 1991 coup.

[25] The Soviet Union collapsed by the end of 1991,[70] just a few months after Matlock, having fulfilled his ambition when he joined the Foreign Service, retired from a diplomatic career spanning 35 years.

[9] After retirement from the Foreign Service, Matlock began work on his magnum opus, Autopsy on an Empire: The American Ambassador's Account of the Collapse of the Soviet Union.

[71] A subsequent book, Reagan and Gorbachev: How the Cold War Ended[3] describes the relationship of the two men and their efforts to reach agreement on arms reductions between the superpowers.

"[72] Reagan, according to Matlock, never altered from his goals as annunciated at his first press conference as president when he stated that, appearances to the contrary, he was in favor of "an actual reduction in the numbers of nuclear weapons.

[74] His third book, Superpower Illusions: How Myths and False Ideologies Led America Astray--And How to Return to Reality,[75] published in 2010, provides an analysis of the post Cold War period along with his policy prescriptions.

[78] On Jan 4, 2007, Matlock joined with George Shultz, William Perry, Henry Kissinger and Sam Nunn to advocate a goal of a world free of nuclear weapons.

[79] On 23 September 2008 after a two-day conference at the Carnegie Endowment for International Peace, he joined several other former ambassadors to issue a joint statement on how Russia and the United States might move forward in their relations.

[81] Matlock has also signed an open letter of May 13, 2011 asking the implementors of the New START treaty between the U.S. Russia to make public the locations and aggregate numbers of nuclear weapons, in order to promote transparency and reduce mistrust.

[82][83] On Jan 18, 2011 he co-signed an open letter to President Obama urging a United Nations resolution condemning Israeli settlements in the occupied territory.

[86][87] In late 2021, he argued that Ukraine is a state but not yet a nation, because of its deep ethnolinguistic divisions, saying it "has not yet found a leader who can unite its citizens in a shared concept of Ukrainian identity.

"[91] Having witnessed the Cuban Missile Crisis of 1962 from the inside the American Embassy in Moscow, he was acutely aware of the potential dangers of seeming to threaten the security and even the identity of a nuclear-armed state.

[92] He considered the war aims on both sides of the conflict to be unrealistic and urged a cease-fire and diplomatic settlement that would end the loss of Ukrainian and Russian lives and destruction of property in much of Ukraine.

Furthermore, in denying that Russia has a "right" to oppose extension of a hostile military alliance to its national borders, the United States ignores its own history of declaring and enforcing for two centuries a sphere of influence in the Western hemisphere.