Diogo de Carvalho e Sampayo (28 May 1750 – 29 December 1807)[1] was a Portuguese nobleman, magistrate, diplomat and scientist.

A knight of the Order of Malta and a judge by profession, Carvalho e Sampayo became notable as an amateur scientist who authored two important works on the subject of chromatics.

[1] He graduated from the University of Coimbra where he studied Law, later, in 1783, serving as a judge in Viana do Castelo.

[2] Johann Wolfgang von Goethe was familiar with Carvalho e Sampayo's work: his seminal treatise Theory of Colours (published 1810) includes a general assessment of Sampayo's 1791 book Memória sobre a Formação Natural das Cores ("An Essay on the Natural Formation of Colours").

[3] Starting in 1789, he moved to Madrid where he headed the Portuguese diplomatic representation there, first as chargé d'affaires, then as a minister plenipotentiary, and finally as ambassador extraordinary, returning definitely to Portugal in 1801.