Mengs was born in the northern Bohemian town of Ústí nad Labem (German: Aussig) into the Lutheran family of Danish painter Ismael Mengs, a hofmaler (court painter) at the court of the Saxon-Polish electors and kings.

In an effort to conceal the birth of their illegitimate child, he decided to take her along with him on a "vacation" to the nearest bigger town abroad.

After a few weeks, Mengs took his child and her mother back to Dresden, the Saxon capital, where they lived.

In 1765, she married Anton von Maron, an Austrian-born portrait painter and pupil of her brother.

Among her pupils were Apollonia Seydelmann, her niece Anna Maria Mengs, and Sofia Clerc.