Spasovich went to school in Minsk and studied law in St. Petersburg University, where he later became a professor. After the government persecuted some of his students in 1861, Spasovich resigned his professorship in protest. Two years later, his textbook on criminal law was banned.
After the Judicial reform of Alexander II he emerged as a leading trial lawyer. He took part in many of the sensational political trials of the 1860s and 1870s, including the Nechayev process. Fetyukovich, a defense attorney in Dostoyevsky's Brothers Karamazov, was apparently based on Spasovich.
Spasovich was one of those who tried to bring Russia and Poland together. He founded in St. Petersburg the Polish-language newspaper Kraj and "advocated the concept of Polish cultural autonomy within Russia" in the Warsaw periodical Atheneum.