He was born in Geneva, then in the independent Republic of Geneva, where he studied portrait miniature painting. Having acquired its first rudiments, he went to Paris in 1744. There he gained great proficiency in the art. He lived there studying and painting until 1750. Then he returned to his native place and practised his profession for some years. In 1756, he again went to Paris. In 1760, he went to England, where he was executed in Haymarket, London, for murdering his landlady Anne King.
- George Henry Borrow Celebrated Trials, and Remarkable Cases of Criminal Jurisprudence: Volume 4 1825 Page 400 THEODORE GARDELLE .. was a native of Geneva, and having received a university education, went to Paris, where he studied miniature-painting, and havin made great proficiency in the art, returned to ...
- The Annual Register 1758 - Page 43 "Gardelle, Theodore, who was executed for the murder of mrs. Anne King; narrative of the fact for which he suffered, and some account of the character of mrs. King, as well as the murderer,
- The Gentleman's and London Magazine 1741 -- Page 145 "Some Account of Theodore Gardelle, who was lately executed for the murder of Anne King. THeodore Gardelle, a native of Geneva, was born in the year 1722. At about the age of 14, his father put him apprentice to an engraver and embosser ..."
- Theodore Gardelle, exclassics.com