He married Sofia Katarina di Dosmo, daughter to an Italian employee of the royal stables, and became the father of actor Carl Edvard Hjortsberg (1804–1857) and father-in-law of Fanny Westerdahl.

He was noticed by the theatrically interested King Gustav III of Sweden, who saw a great dramatic talent in him, and hired him at the royal court as a so-called garçon bleu, a common (non noble) page boy, reader and librarian.

Lars Hjortsberg made his debut at the Royal Swedish Opera at the age of six in 1778, when he played an angel with a couple of lines at the celebration of the birth of the Crown Prince in Athalie.

In 1787, he was enrolled in the Royal Dramatic Training Academy, and performed in a student play for the king the same year.

The building was with narrow passages and only one exit which could have led to many casualties if Hjortsberg had not directed the evacuation with such calmness and efficiency that no one was killed, which made him a hero in the eyes of the public, who greeted him with great applause at his next performance at the building at the Royal Swedish Opera, where the Royal Dramatic Theatre would now also be located.