Peter Berthelot was born in Honfleur (Calvados, France) on December 12, 1600 and at a very young age he gave himself to navigation, traveling to Spain, England, America. In 1619 he went to India, where, as a cosmographer and first pilot of the kings of France and Portugal, he distinguished himself by his worth and ingenuity, as evidenced by his Maritime Tables, outlined with great skill and preserved in the British Museum (Ms. Sloan 197).

In 1635, finding himself in Goa, on the advice of his spiritual director, Fr. Philip of the Most Holy Trinity, he entered the Discalced Carmelites, where he was professed on December 25, 1636 and given the name of Denis of the Nativity and received the priesthood on August 24, 1638. Both in the novitiate and after profession, according to the testimony of Fr. Philip, he was an example of virtue to all the religious. During prayer, he was not infrequently raised to divine contemplation, appearing to be surrounded by heavenly splendour. In 1638, the Viceroy Pietro da Silva sent to the Sultan of Achén (Sumatra), the ambassador Francesco de Souza de Castro who wanted Denis with him as a spiritual guide and as an expert on the sea and the Malay language. Denis took as his companion Thomas Rodriguez, who, born about 1598 in Portugal, had entered the same Order as a lay brother, with the name of Redemptus of the Cross. 

The two left Goa with the legation on September 25, 1638, and, after fortunate navigation, on October 25 they arrived at Achén, where, greeted with signs of simulated joy, they were soon taken prisoner. As religious, Denis and Redemptus were tormented and tempted more than the others to leave their Catholic faith and convert to that of the Muslims. In prison Denis deprived himself of necessities out of charity towards others, whom he supported with words, help and example. After the death sentence, Redemptus died among the first, while Denis suffered martyrdom last, at his desire, in order to be able to comfort the others: he was killed by a sword, which split his head in two, on November 29, 1638.

The beatification ceremony was held on June 10, 1900.