Rabbi Dov Ber, known as the Maggid of Mezritch, was born in Lukatch, near Rovno in Volhynia, to Rabbi Avraham, a poor schoolteacher. His year of birth is uncertain: 1704 is often given, but traditions place it between 1690 and 1710. According to Chassidic tradition, when the family home burned down together with the genealogical scroll tracing the family back to Rabbi Yochanan HaSandlar, the boy comforted his mother by promising that a new lineage would begin with him.

He studied in Lvov at the yeshiva of Rabbi Yaakov Yehoshua Falk, author of the Pnei Yehoshua. After marrying Kayla, daughter of Shalom Shachna of Torchin, he served as a teacher in a nearby village, lived in great poverty and delved into Kabbalah. He later became a preacher (maggid) in Torchin, Korets and Rovno, renowned for the power of his words. Around 1740 his son, Rabbi Avraham HaMalach, was born.

One account relates that his poor health led him to seek out the Baal Shem Tov, of whom he became one of the closest disciples. After the Baal Shem Tov's passing on Shavuot 5520 (1760), he led the Chassidic movement from Mezritch, which became its center. Unlike his teacher, he seldom traveled, instead sending his disciples to spread the teaching throughout Poland and beyond.

His teaching stressed cleaving to God (devekut) and doing every act for the sake of Heaven. He trained the circle of disciples who founded most Chassidic dynasties: Rabbi Elimelech of Lizhensk, Rabbi Zusha of Hanipol, Rabbi Levi Yitzchak of Berditchev, Rabbi Shneur Zalman of Liadi, whom he charged with composing a new Shulchan Aruch, and many others.

He wrote no books himself; his words were recorded by his disciples. Works: Maggid Devarav LeYaakov (Korets, 5541 / 1781), Or Torah (Korets, 5564), and other collections such as Or HaEmet and Kitvei Kodesh.

In 5532 he returned to Rovno; shortly before his death, fleeing an epidemic, he settled in Annopol (Hanipol), where he passed away on 19 Kislev 5533 (15 December 1772). He is buried there in an ohel beside Rabbi Zusha of Hanipol.