Polák was born in Karlovy Vary and grew up in Marxist–Leninist Czechoslovakia. He became a dissident in his teens, when he became involved in the Prague Spring of 1968, and as a consequence he was not permitted to attend university. He took part in various dissident and underground movement activities. He was a co-founder of the 1989 strike committee that led to the Velvet Revolution. He was also involved with the Czech branch of the Movement for Civil Society.