Klingberg made major contributions in the fields of infectious and noninfectious disease epidemiology and military medicine, while simultaneously passing intelligence to the Soviet Union regarding Israel's biological and chemical warfare capacities.

Declared the "most important Soviet spy in Israel" by the Jerusalem Post, Klingberg is regarded as causing the greatest damage ever to the country's national security interests.

Paroled to home detention in 1998 due to ill health, he was permitted to move to Paris in 2003 to live with his daughter on the condition that he never speak of his work in the areas of biological and chemical weapons.

In 1939, with the German invasion of Poland, Klingberg's father urged him to flee to the Soviet Union, completing his medical studies in Minsk in 1941.

[10][4] While living in post-war Poland, Klingberg met Adjia Eisman, who went by the name Wanda Jasinska, a survivor of the Warsaw Ghetto.

Some sections of Shin Bet believed the immigration to have been prompted by Soviet intelligence, but Klingberg strongly denied this, saying he was motivated by the loss of his family in Poland during the Holocaust.

[10] Klingberg's academic career and research papers earned him an international reputation in his field, and he was invited to conferences by the World Health Organization.

[4] He was president of the European Teratology Society (1980–1982) and a co-founder and chairman (1979–1981) of the International Clearinghouse for Birth Defects Monitoring Systems (ICBDMS).

Klingberg passed information on Israel's chemical and biological weapons research, frequently using the Russian Orthodox Church in Abu Kabir as his contact point with the KGB.

[4][19][12] In the 1950s, Klingberg was secretly awarded the Order of the Red Banner of Labour, at the time the Soviet Union's second highest honour, in recognition of his services.

[6] Klingberg has indicated that sometime around the mid-1950s he considered ceasing to pass information to the Soviets, but he concluded that the relationship would become coercive and that he preferred to "maintain voluntary relations.

[22] Israel's foreign and domestic intelligence agencies, Mossad and Shin Bet, began to suspect Klingberg of espionage in the 1960s, but shadowing brought no results.

In 1965, he passed a polygraph test, according to Israeli journalist Yossi Melman, due to the fact that his interrogators simply asked the wrong questions, as they suspected he was spying for Polish rather than Soviet intelligence.

[23] In 1972, a newly arrived Jewish migrant from the Soviet Union admitted to working for the KGB during Shin Bet screening, and he became double agent for the agency.

[24][23] In January 1983, Shin Bet officers informed Klingberg they wanted to send him to Southeast Asia, where a chemical plant had allegedly exploded.

After ten days, Klingberg admitted to passing intelligence to the Soviets and signed a confession indicating he had been blackmailed into spying.

For the first 10 years of his sentence, he was held in solitary confinement in a high-security prison in Ashkelon under a false identity as a publisher named Abraham Grinberg.

[29][21] Due to the investigations of British journalist Peter Pringle, Israeli authorities acknowledged Klingberg's conviction and imprisonment in 1988.

[4][32] Interviewed in 2008, Klingberg maintained that he had spied out of ideological reasons, but had lied to his interrogators as he believed claiming to have been blackmailed would result in lighter treatment.

[28] In January 2003, Klingberg was released from house arrest and immediately left Israel for Paris to be with his daughter Sylvia and grandson Ian Brossat.

[28] Klingberg's spying and imprisonment affected the life of his grandson, Ian Brossat, a politician elected to the French Senate in September 2023.

[37] In 2009, when he won a seat on the Council of Paris, Brossat noted how his political opponents attempted to tarnish him by association with Klingberg.