Franjo Kresnik graduated from the Croatian Grammar School in Rijeka, and then studied medicine in Vienna and Innsbruck. He began his medical career in children’s hospitals in Vienna and Innsbruck. Kresnik returned to Rijeka in 1900, where he worked as a well-known and respected doctor for the rest of his life.
Besides being a prominent physician, he had a profound interest in music. For almost 40 years he diligently and persistently studied the ancient Italian art of building instruments (liuteria). He founded a laboratory in Rijeka where he spent his free time in research and practical work. He studied some of the most famous masters from Cremona (Amati, Guarneri, Stradivari), and with his assistant Carl Schuavi, made over fifty violins and one string quartet.
He also wrote several notable essays and dissertations on string instruments. As an excellent connoisseur of the instruments of the old masters in Cremona, he was known as "the man who reads violins" - the most famous Croatian violin maker, also known as the Croatian Stradivarius.