Arne Treholt, a charismatic rising star in the Norwegian foreign-policy establishment who was convicted in 1985 of passing government secrets to the Soviet Union and Iraq, died on Sunday in Moscow. He was 80.
His death, after a short illness, was first reported in the newspaper Aftenposten, which said it had received confirmation from Mr. Treholt’s family.
The Treholt scandal is widely considered the most significant espionage case in modern Norwegian history, and one of the most damaging of the Cold War. It emerged as tensions were rising between NATO countries and the Soviet Union, particularly along Europe’s so-called Northern Flank, with Norway at the center.
Given Mr. Treholt’s status as a promising and idealistic future leader, the case drew comparisons to those of Alger Hiss in the United States and Günter Guillaume, an aide to Chancellor Willi Brandt of West Germany whose exposure as a spy forced Mr. Brandt to resign.
The scandal also exacerbated a generational rift in Norwegian society. Mr. Treholt was an ardent left-wing politician who emerged from the anti-American, anti-militarist sentiment of the 1960s, and who often clashed with older, pro-Western establishment leaders, even before his arrest.
Mr. Treholt was sentenced to 20 years in prison, the maximum allowed under Norwegian law, and he admitted that he had passed information to his Soviet handlers. But he insisted that he was not a spy.
Rather, he said, he did what he did to improve communication and lower tensions between nuclear-armed antagonists — although the large cash payments he received into a secret Swiss bank account, and the fact that the Iraqis also paid him for his services, undermined his case.
For a time in the late 1970s and early ’80s, Mr. Treholt looked like a prime minister in the making. A former journalist, he had entered politics and quickly climbed the ranks under the tutelage of Jens Evensen, a respected lawyer who held a string of ministerial positions. He was dashing — he was partial to double-breasted white suits — and married to Kari Storaekre, a well-known television personality.
“Arne Treholt was the perfect political man,” Aftenposten wrote in a 1985 profile.
Mr. Treholt was in the middle of many of Norway’s most important foreign-policy engagements of the 1970s, including trade negotiations with the European Community, talks with the Soviet Union over their shared maritime border, and Norway’s leadership on environmental policy in the United Nations.
In the early 1980s, as the head of the press office for the Ministry of Foreign Affairs, he arranged for diplomatic visits and was therefore privy to confidential conversations between Norway’s leaders and its closest allies.
But since the mid-1970s, he had been passing much of the information he gleaned in his various positions to Gennady Titov, a K.G.B. agent based in Oslo. He handed over plans for Norway’s defense against Soviet invasion, the location of NATO weapons, and the minutes from meetings between the prime minister and the foreign minister.
He was arrested at the Oslo airport in early 1984, just before boarding a flight to Vienna, where he was to meet Mr. Titov. In his briefcase were some 65 confidential documents.
After his initial claim of wayward idealism failed to sway the court, Mr. Treholt offered another: sexual blackmail. He said that a party he attended in Moscow in 1975 had evolved into an orgy, and that a Soviet agent later presented him with compromising photos.
Mr. Treholt’s conviction came quickly, but doubts remained. The government had insisted on holding some of the trial in secret, to protect confidential information. That fueled questions about the legitimacy of the evidence against him, especially when he was released and pardoned in 1992 after serving just eight years of his sentence.
He moved to Russia and later to Cyprus, started a lucrative second career as an investor and importer, and tried to get his case reopened. But the Norwegian courts refused, and he eventually settled in Moscow.
Arne Treholt was born on Dec. 13, 1942, in Brandbu, about 50 miles north of Oslo. His father, Thorstein, was a politician who served as agriculture minister when Arne was young, and his mother, Olga Lyngstad, was a homemaker.
Mr. Treholt studied politics and economics at Oslo University and, after graduation, worked as a journalist for Arbeiderbladet, the official newspaper of the liberal Norwegian Labor Party. He also became active in pro-democracy efforts in Greece, where a right-wing coup had established a military dictatorship in 1967.
It was through that activism that he met Mr. Evensen — as well as his first contacts in the K.G.B.
Mr. Evensen hired him as his secretary. Mr. Treholt later served in the Bureau of Maritime Affairs, the Norwegian delegation to the United Nations in New York and the Ministry of Foreign Affairs.
Mr. Treholt’s first two marriages, to Brit Sjorbotten and Ms. Storaekre, ended in divorce. While in prison he married Renee Steele, a fellow inmate less than half his age. Dying of AIDS, she received compassionate release in 1992 and died a few months later. He was allowed to leave prison to attend her funeral, and he was pardoned shortly after.
Mr. Treholt is survived by his son, Torstein Storaekre, and two grandchildren.
Norwegian authorities began to suspect Mr. Treholt in the early 1980s, thanks in part to tips from Soviet defectors. The F.B.I. trailed him in New York, and his Oslo apartment was inspected twice, both times revealing large piles of cash, which authorities left in place in order not to alert him to their investigation.
Mr. Treholt was the author of three memoirs, the first of which, “Alene” (“Alone”), he wrote in prison and smuggled out to a publisher. It appeared in 1985, sold well and even won a minor literary prize. He also translated Isaac Asimov’s science fiction novel “Foundation” from English into Norwegian.
After his release, Mr. Treholt received the equivalent of about $100,000 from an anonymous donor, money he used to start a new life in Russia. Along with his investment activities, he became an advocate for Russian interests; most recently, he wrote articles defending the Russian invasion of Ukraine.
Mr. Treholt never ceased insisting on his innocence. But his case was further undermined last year, when researchers at the Center for Cold War Studies, a Danish think tank, uncovered K.G.B. documents discussing his status as a valuable source of confidential information.
In assessing his motivation, one document described it as “an ideological-political basis, supplemented by material goods.”