He met St. Dominic while the saint was traveling with Bishop Diego. The two became lifelong friends and Bertrand assisted in convincing Dominic to join him in fighting heresy. Bertrand was one of the first to join the new Dominican order, taking the habit at Toulouse in 1216. He served as St. Dominic's right hand man, even taking charge of the order while Dominic travelled to Rome to seek papal approval for the order.
Bertrand was later sent on mission to Paris with Matthew of France. These two established and governed the first Dominican foundation at Paris where they developed the Dominican scholarly tradition.
In his later years Bertrand was appointed provincial of Provence. He was known for working miracles, for his austerity and holiness, and his humility. So great were his gifts that some began to refer to him as a second Dominic.
In 1230, Bertrand had travelled on mission to Garrigue to preach to the Cistercian sisters of St. Mary of the Woods. While on this trip he fell ill and passed away. The sisters buried him in their cemetery until it became clear from the vast number of pilgrims coming to visit his tomb, that Bertrand needed a more suitable burying place. Unfortunately, his relics were destroyed during the protestant revolution. Bertrand was beatified by Pope Leo XIII on July 14, 1881.