From 1750 to 1753, Justi taught at the Theresianum Knights Academy in Vienna, Austria, where he established close contacts with Friedrich Wilhelm von Haugwitz whose administrative reforms exerted a strong influence on his political ideas.
Justi's oeuvre consists of more than 50 independent works dealing with philosophical, literary, technological, geological, chemical, physical as well as political and economic issues.
Writing against the background of the European power struggle during the Seven Years' War, Justi's central aim was to create modern commercial monarchies in the larger states of the Holy Roman Empire that could equal the military strength, political standing and economic performance of England and France.
In his political writings, Justi stressed that a country could only be economically and commercially successful if it was run by a moderate government that recognised the inviolability of private property.
Apart from measures supporting population growth and fostering competition (by reducing the power of guilds and corporations), Justi viewed the increase in private consumption (by abolishing sumptuary laws), the spread of manufactures and companies as well as the growth in external trade (with the help of government-sponsored trade companies and the abolition of prohibitions regarding the import and export of goods) as cornerstones for economic success.
Research on Justi has primarily focused on his works on political economy (see overview studies by Ferdinand Frensdorff and Ulrich Adam).