Johann Wilhelm Hässler was born in Erfurt. He first learned music from his uncle Johann Christian Kittel, who worked as an organist in the city. Around 1762, Hässler took his first professional job as an organist at the Barfüßerkirche local church. After his father passed away in 1769, Hässler took over running the family fur business but still found time to go on concert tours. In the early 1770s, he toured Germany, and in the 1780s and 1790s, he traveled to many places in Europe for music performances. On April 15, 1789, Hässler competed in an organ contest against Wolfgang Amadeus Mozart in Dresden during Mozart's trip to Berlin. While traveling on these tours, Hässler also met other well-known musicians like Johann Nikolaus Forkel, Johann Adam Hiller, Franz Benda, and Carl Philipp Emanuel Bach. These experiences helped Hässler connect with important figures in the music world of his time. From 1790 to 1792, Hässler lived in London. After that, he moved to Saint Petersburg and then settled in Moscow in 1794. In Moscow, he worked as a respected music teacher and composer. He stayed there until he died, making the city his home for the later part of his life.