Through the late 1970s he became increasingly involved in political cases, defending opponents of the Communist regime, serving as a legal advisor for Solidarity, and assisting in the successful prosecution of the murderers of Jerzy Popiełuszko.

In 1982, he met the film director Krzysztof Kieślowski, who was planning to direct a documentary on political show trials in Poland under martial law.

Piesewicz returned to his law career, but remained in touch with Kieślowski and three years later persuaded him to create a series of films based on the Ten Commandments.

This series, Dekalog, explored the filmmakers' mutual interest in moral and ethical dilemmas in contemporary social and political life, and achieved (belated) critical acclaim around the world.

Their later collaborations, The Double Life of Véronique and Three Colours (Blue, White, Red), focused on metaphysical questions of personal choice and appeared relatively apolitical, though the latter series was based on Piesiewicz's idea of dramatizing the French political ideals of liberty, equality, and fraternity in the same way they had previously dramatized the Ten Commandments.