Blondeau was born into a merchant family from Montreal in New France.
In 1757, during the French and Indian War, he went into the employ of Joseph-Michel Cadet,[1] who was purveyor general with the French forces in New France, and spent a year at Fort St. Frédéric on Lake Champlain.
He then organized trading trips to Grand Portage (Minnesota) and Fort Michilimackinac (near present-day Mackinaw City, Michigan) for his father.
Blondeau became an important businessman in Montreal and was actively involved in a variety of real estate endeavors.
He partnered with Joseph Quesnel[2] on a number of business ventures.