[1] Saint-Castin was born at Escout, Béarn, France, to Jean-Jacques d'Abbadie and Isabeau de Béarn-Bonasse,[2] the youngest of three sons.

He left for Canada at the age of thirteen as an ensign in the army, as was suitable for the youngest son of a noble.

After he returned from Boston, Governor Frontenac gave Castin the task of allying the Abenaki with the French and recaptured the former capital of Acadia, Fort Pentagouet the following year (1675) during King Philips War.

He took this role seriously and, while he became the third Baron de Saint-Castin on the death of his elder brother that year, he appears to have devoted his time to becoming an Abenaki.

"[5] Menneval suggests polygamy and some recent historians have upheld this view, at least insofar as Saint-Castin having married more than one daughter of Madockawando.

[6] Writing a brief account of Saint-Castin within a decade of Menneval's account, Baron de Lahonton makes a point of countering rumours that Saint-Castin was a polygamist: “He has several daughters, who are, all of them, married very handsomely to Frenchmen… He has never changed his wife, by which means he meant to give the savages to understand, that God does not love inconstant folks.”[7] Lahanton's itinerary, as he recorded it, did not take him to the Penobscot region.

Thus the “several daughters” already married by this time would seem to precede Castin's marriage in Penobscot in 1684, said to have been blessed by a Jesuit missionary.

At some point prior to departure, Saint-Castin seems to have buried a large treasure of silver coins on a bank of the Bagaduce River, but without telling family or friends.

In 1714, Saint-Castin's son, Bernard-Anselme sailed to France with his wife Marie-Charlotte Damours de Chauffours and daughter.