In the early 1750s he returned to Geneva, where he received the title of Professor Emeritus of Medicine, and later moved to Paris, where he opened a medical practice in 1766.

Tronchin was an influential 18th-century physician, whose popularity spread amongst European royalty and the upper classes.

Tronchin is mentioned in passing as a great physician in the Marquis de Sade's "Philosophy in the Bedroom".

[4] He was distrustful of traditional medical practices such as bloodletting and purging, and was an advocate of a simple and natural hygiene that stressed fresh air, diet and exercise.

He was scornful of a sedentary lifestyle and excessive sleep, and dedicated several hours of the week to medical assistance for the poor.