Erik Magnus was born on 25 October 1749 as the seventh child of Mathias Gustav Staël von Holstein, the scion of an ancient noble family originally from the Rhineland.

Staël's charming manners, good looks and affable disposition soon impressed Creutz and many members of the French court, including Queen Marie Antoinette herself.

He obtained a dowry of 650,000 livres, was made permanent Swedish ambassador to the Court of Louis XVI, and was invested with the Order of the Polar Star.

Staël had a stormy relationship with Gustav III and he often found himself caught between the interests of his politically active and liberal wife, the ever-changing government of Republican France, and the counter-revolutionary position of the King of Sweden.

Staël successfully negotiated the cession of Saint Barthélemy[8] to Sweden and supported the proposal of William Bolts for a Swedish colony in the eastern Indian Ocean.