Merton wrote more than 50 books in 27 years, mostly on spirituality, social justice, and quiet pacifism, as well as scores of essays and reviews. Among his most enduring works is his bestselling autobiography, The Seven Storey Mountain (1948). Merton's account of his spiritual journey inspired scores of World War II veterans, students, and teenagers to explore monasteries' offerings across the US. The Seven Storey Mountain is on National Review's list of the 100 best nonfiction books of the century.

Merton became a keen proponent of interfaith understanding, exploring Eastern religions through his study of mystic practice. His interfaith conversation, which preserved Protestant and Catholic theological positions, helped build mutual respect via their shared experiences during heightened hostility.

Merrton is known for pioneering dialogue with prominent Asian spiritual figures, including the Dalai Lama, Japanese writer D. T. Suzuki, Thai Buddhist monk Buddhadasa, and Vietnamese monk Thich Nhat Hanh. He traveled extensively to meet with them and attend international conferences on religion. In addition, he wrote books on Zen Buddhism, Confucianism, and Taoism and how Christianity is related to them. This was highly unusual in the United States, particularly within the religious orders.