He was born in Paris, France, as Jacques d'Adelswärd, on 20 February 1880.
As he was related on his paternal side to Axel von Fersen, a Swedish count who had had a supposed relationship with Marie Antoinette, D'Adelswärd took on the name Fersen later in his life to advertise his link with his distant relative.
D'Adelswärd's grandfather had founded the steel industry in Longwy-Briey.
Adelsward went to school in Paris and studied briefly there at the Ecole des Sciences Politiques, and afterward at the University of Geneva.
His mother Louise Emilie Alexandrine Vührer (1855-1935) came from a Catholic Alsatian family.
D'Adelswärd's maternal grandfather, Thomas Michel Alexandre Vührer (c. 1817-1886), was a referendary at the French Ministry of State, director of Le Paris-Journal as well as founder of the Parisian newspaper Le Soi.
Jacques' father died when he was seven years old.
He was assigned a guardian, who was a friend of the family - Viscount Elie Marie Audoin de Dampierre (1846-1909).
During his teenage years, the family spent long summer vacations at his grandfather's estate on Jersey, where Jacques reportedly had an intimate encounter with a blond Eton schoolboy.

In 1897 he visited Capri and other parts of Italy with his mother.
The family steel furnaces had become profitable enough to make Jacques d'Adelswärd a rich and 'eligible' bachelor when he inherited at the age of 22.
Apart from joining the military, he traveled extensively and settled down as a writer.
He published Chansons Légères (1900) and Hymnaire d'Adonis (1902) and other poems and novels.
In 1902 he holidayed in Venice, where he associated with the novelist Jean Lorrain.
On his return to Paris, he published his novel, Notre Dame des mers mortes.
He was born in Paris, France, as Jacques d'Adelswärd, on 20 February 1880. As he was related on his paternal side to Axel von Fersen, a Swedish count who had had a supposed relationship with Marie Antoinette, D'Adelswärd took on the name Fersen later in his life to advertise his link with his distant relative. D'Adelswärd's grandfather had founded the steel industry in Longwy-Briey. Adelsward went to school in Paris and studied briefly there at the Ecole des Sciences Politiques, and afterward at the University of Geneva. His mother Louise Emilie Alexandrine Vührer (1855-1935) came from a Catholic Alsatian family. D'Adelswärd's maternal grandfather, Thomas Michel Alexandre Vührer (c. 1817-1886), was a referendary at the French Ministry of State, director of Le Paris-Journal as well as founder of the Parisian newspaper Le Soi. Jacques' father died when he was seven years old. He was assigned a guardian, who was a friend of the family - Viscount Elie Marie Audoin de Dampierre (1846-1909). During his teenage years, the family spent long summer vacations at his grandfather's estate on Jersey, where Jacques reportedly had an intimate encounter with a blond Eton schoolboy. 
In 1897 he visited Capri and other parts of Italy with his mother. The family steel furnaces had become profitable enough to make Jacques d'Adelswärd a rich and 'eligible' bachelor when he inherited at the age of 22. Apart from joining the military, he traveled extensively and settled down as a writer. He published Chansons Légères (1900) and Hymnaire d'Adonis (1902) and other poems and novels. In 1902 he holidayed in Venice, where he associated with the novelist Jean Lorrain. On his return to Paris, he published his novel, Notre Dame des mers mortes.
Jacques d'Adelswärd-Fersen