A "pessimistic freethinker", al-Maari was a controversial rationalist of his time, citing reason as the chief source of truth and divine revelation. He was pessimistic about life, describing himself as "a double prisoner" of blindness and isolation. He attacked religious dogmas and practices, was equally critical and sarcastic about Judaism, Christianity, Islam and Zoroastrianism, and became a Deist. He advocated social justice and lived a secluded, ascetic lifestyle.