The article introduces readers to Joseph Ronczewski (1864-1921) who was born in St.Petersburg. He is the brother of the well-known sculptor and specialist of the history of architecture Professor Konstantin Ronczewski. Until now, Joseph Ronczewski had been in the shadow of his brother Konstantin and his name is not well known, therefore the research about his life has been done. He is an alumnus of the Department of Chemistry of Riga Polytechnic (he graduated in 1889) and from 1893 to 1896, was an Assistant with the same Department. He perfected his knowledge in steel industry in Germany and later was a professor and librarian with the Institute of Technology (1900-1905) in Tomsk. He carried out his research in the sector of metallurgy. During World War I, he was in Russia and after the war moved to Latvia. In February 1921, he was the first to head the Department of the Polish Minority of the Ministry of Education of Latvia. He died in December 1921.