Johann Carl Loth apprenticed under his father, Bavarian court painter Johann Ulrich Loth, who had been deeply influenced by Roman painting of the 1600s. Johann Carl himself went to Rome at some point after 1653. By 1656 he was in Venice, where he remained for life and became one of the most well known Venetian painters of his day.
In Venice, Loth worked under Giovanni Battista Langetti, a follower of Luca Giordano, under whom he discovered the art of naturalism and tenebrism that had originated with Caravaggio. Loth incorporated those effects along with Langetti's dramatic chiaroscuro; having found his own style, he deviated little from it for the rest of his career. Loth primarily painted altar and easel pictures dominated by the nude figure. The Holy Roman Emperor Leopold I and other monarchs and ambassadors purchased many of his paintings. His Venetian studio became a virtual "picture factory" to meet the great demand for his paintings. In 1692 he was appointed court painter to the Emperor.