In the nineteen fifties he studied in the Faculty of Law at Lomonosov University in Moscow where he was a classmate of Michail Gorbacov. After graduation he became a research worker at the Czechoslovak Academy’s Science Institute of State and Law. In 1963 he became senior lecturer at the Charles University’s Faculty of Law. Here he applied himself to history of political theories and comparative research of political systems. He was also head of the team that was dealing with issues of socialism development.
He was a member of the Communist Party since 1946 and became a member of the Communist Party’s Central Committee in March 1968 when he immediately became involved in the reformist movement. He was an author of the political part of Action Program, participated on Moscow negotiations in August 1968 and signed Moscow protocols. In November 1968 he was withdrawn from top functions because of his disapproval with progressing normalisation. Subsequently he was also withdrawn from Central Committee and in 1970 expelled from Czechoslovakian Communist Party.
He was able to stay in the Institute only for few months then he was transferred to entomology department of Prague’s National Museum. In 1976 Mlynar became one of the first initiators and signatories to Charter 77. As a result he was from January to June 1977 kept under house arrest and eventually he left the state for Austria where he worked as a publicist and political scientist. He became a leading research worker of Austrian Institute for International Politics in Luxenburg and Professor of political science at University in Innsbruck. Subsequently he established himself as an internationally recognized expert on development tendencies of Soviet regimes and later on so called Perestroika.
After November 1989 he came back to his home country and was trying to influence politics from the position of a left democrat (from 1995 to 96 he was an honorary president of Left Bloc).
He regularly published in left oriented Rude pravo (later Pravo) papers and also published few books (Crisis in Soviet systems from Stalin to Gorbachev, 1991; Free Lance Socialist, 1992; Reformists are usually not happy, 1994). The biggest attention he received was his memoirs Night Frost in Prague (Cologne in 1978, Prague 1990; translated to 11 languages) that describes Czechoslovakian events of the years 1968-69.