Marchenko, originally an apolitical oil driller from a poor background, turned to writing and politics as a result of several episodes of incarceration starting in 1958, during which he began to associate with other dissidents. Marchenko gained international fame in 1969 through his book, "My Testimony", an autobiographical account written after his arrival in Moscow in 1966 about his then-recent sentences in Soviet labour camps and prisons. After limited circulation inside the Soviet Union as "samizdat", the book caused a sensation in the West after it revealed that the Soviet gulag system had continued after the death of Joseph Stalin. In 1968, in the run-up to the Soviet invasion of Czechoslovakia, Marchenko wrote an open letter predicting the invasion. Arrested again, he was released in the early 1970s, but in 1974 he was interrogated and internally exiled to Irkutsk Oblast. In 1976, Marchenko became one of the founding members of the Moscow Helsinki Group, before being again arrested and imprisoned in 1981, where he kept writing throughout his prison time, publicizing the fate of Soviet political prisoners. Having spent about 20 years in all in prison and internal exile, Nathan Shcharansky said of him: "After the release of Yuri Feodorovich Orlov, he was definitely the number one Soviet prisoner of conscience." becoming one of the Soviet Union's "perpetual prisoner[s]".