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.
Pada 1976, Marchenko menjadi salah satu anggota pendiri Moscow Helsinki Group, setelah ditangkap dan ditahan lagi pada 1981, dimana ia tetap menulis selama masa penahanannya, yang mempublikasikan nasib para tahanan politik Soviet.