Guillaume Barthez de Marmorières (2 March 1707 – 11 January 1799) was a French civil engineer.

He was elected to the Académie des sciences et lettres de Montpellier (fr), gained a wide reputation through either his writings or the works he supervised.

He was called upon to edit or contribute two entries in the Encyclopédie of Diderot and d’Alembert.

[1] He was made a hereditary nobleman de Marmorières in 1780 by letters patent of Louis XVI.

[2] He was the father of Paul Joseph Barthez physician, physiologist and encyclopedist who developed the biological theory known as vitalism.