Born in Nogent-le-Rotrou, Soissons joined the Catholic League during the French Wars of Religion despite his older half-brothers' Protestant affiliations.

After the battle of Ivry he led the king's cavalry in besieging Paris in 1590, and proved his worth at the sieges of Chartres in 1591 and of Rouen in 1592.

Although he briefly joined in the scheme of his brother Charles, Cardinal de Bourbon, to form a third party in the kingdom, he attended Henry's coronation in 1594.

[6] The death of Henry IV in 1610 weakened Samuel de Champlain's chances of successfully colonizing New France, and, by the advice of Pierre Dugua, Sieur de Mons, he sought a protector in the person of the Count of Soissons, who accepted the proposal to become the “father of New France,” obtained from the queen regent the authority necessary to preserve and advance all that had been already done, and appointed Champlain his lieutenant with unrestricted power.

[7] As the youngest son of a cadet branch of the royal dynasty, Louis could not expect a large patrimony, but was allotted the countship of Soissons from among the Bourbon estates inherited from his paternal great-grandmother, Marie de Luxembourg.