Mengs was born in 1728 at Ústí nad Labem (German: Aussig) in Bohemia. His father, Ismael Mengs, a Danish painter, established himself finally at Dresden, whence in 1741 he took his son to Rome.

In Rome, his fresco painting of Parnassus at Villa Albani gained him a reputation as a master painter. The appointment of Mengs in 1749 as first painter to Frederick Augustus, elector of Saxony, did not prevent his spending much time in Rome, where he had married Margarita Guazzi who had sat for him as a model in 1748, and abjured the Protestant faith, and where he became in 1754 director of the Vatican school of painting, nor did this hinder him on two occasions from obeying the call of Charles III of Spain to Madrid. There Mengs produced some of his best work, and specially the ceiling of the banqueting hall of the Royal Palace of Madrid, the subject of which was the Triumph of Trajan and the Temple of Glory. Among his pupils there was Agustín Esteve. After the completion of this work in 1777, Mengs returned to Rome, and there he died, two years later, in poor circumstances, leaving twenty children, seven of whom were pensioned by the king of Spain. His portraits and self - portraits recall an attention to detail and insight, often lost from the grand manner paintings.

Besides numerous paintings in the Madrid gallery, the Ascension and St Joseph at Dresden, Perseus and Andromeda at Saint Petersburg, and the ceiling of the Villa Albani must be mentioned among his chief works. In 1911, Henry George Percy, 7th Duke of Northumberland, possessed a Holy Family, and the colleges of All Souls and Magdalen, at Oxford, possessed altar - pieces by Mengs's hand.

In his writings, in Spanish, Italian and German, Mengs has put forth his eclectic theory of art, which treats of perfection as attainable by a well - schemed combination of diverse excellences Greek design, with the expression of Raphael, the chiaroscuro of Correggio, and the colour of Titian. He would have fancied himself the first neoclassicist, while in fact he may be the last flicker of Baroque art. Or in the words of Wittkower, In the last analysis, he is as much an end as a beginning.

His intimacy with Johann Joachim Winckelmann, who constantly wrote at his dictation, has enhanced his historical importance, for he formed no scholars, and the critic must now concur in Goethe's judgment of Mengs in Winckelmann und sein Jahrhundert; he must deplore that so much learning should have been allied to a total want of initiative and poverty of invention, and embodied with a strained and artificial mannerism.

Mengs was famous for his rivalry with the contemporary Italian painter Pompeo Batoni. He was also a friend of Giacomo Casanova. Casanova provides accounts of his personality and contemporary reputation through anecdotes in Histoire de Ma Vie.

He died in Rome in June 1779 and was buried in the Roman Church of Santi Michele e Magno.