Gallatin was born in
Geneva, Switzerland, to the wealthy Jean Gallatin and his wife, Sophie Albertine Rollaz. Gallatin's family had great influence in Switzerland, and many family members held distinguishable positions in the magistracy, military, and in Swiss delegations of foreign armies. His parents married in 1753. Gallatin's father, a prosperous merchant, died in 1765, followed by his mother in April 1770. Gallatin, now orphaned, was taken into the care of Mademoiselle Pictet, a family friend and distant relative of Gallatin's father. Here, Gallatin remained, until January 1773 when he was sent to boarding school. Four years later, he suffered the death of his only sister Susanne, who had long been institutionalized with a nervous disorder. Gallatin entered the
Academy of Geneva at the age of fourteen and after finishing with top marks in May 1779, he secretly left Geneva and planned a voyage to
Massachusetts with his classmate Henri Serre in 1780. Gallatin and Serre set sail on
May 27 from
L'Orient, a coastal French commune, in the
Kattie, an American vessel under the command of Captain Loring. The men arrived at
Cape Ann, at the coast of Massachusetts, on
July 14. They traveled to
Gloucester, and then to
Boston on horseback.
Bored of monotonous Bostonian life, the men set sail with a Swiss female companion, to the settlement of
Machias, located on the northeastern tip of the Maine frontier. At Machias, Gallatin operated a bartering venture, in which he dealt with a variety of goods and supplies. He enjoyed the simple life and the natural environment surrounding him. Gallatin and Serre returned back to Boston in October 1781, after abandoning their bartering venture in Machias. Gallatin supported himself by giving French language lessons. Soon afterwards, he sent a letter to Mademoiselle Pictet, offering a frank account of the troubles he was having in America. Pictet sense this would be the case, and she had already contacted Dr. Samuel Cooper, a distinguished Bostonian patriot, whose grandson was a student in Geneva. With Cooper's influence, Gallatin was able to secure a faculty position in July 1782 at
Harvard University, where he would be permitted to teach
French.
Gallatin used his early salary to purchase land in
Fayette County, Pennsylvania, near
Pittsburgh, and he moved there in 1784. In the spring of 1789, Gallatin eloped with Sophia Allegre, the attractive daughter of his landlady, who disapproved of him. However, she fell ill and died later that year. He was in mourning for several years and seriously considered returning to Geneva. However, on November 1, 1793, he married Hannah Nicholson, daughter of the well-connected Commodore
James Nicholson. They would have two sons and a daughter.