Born in the village of Migonys near Kupiškis, in the Grand Duchy of Lithuania. His father was a Lithuanian peasant, Simonas Masiulis, sometimes also called by the name of Stuoka after his stepfather. He was baptized as Laurynas Masiulis. His Lithuanian mother, Kotryna Žekonytė Masiulienė died early in his youth, and her relative and his godmother Anna Gucewicz née Baltušytė, he went to Rome, where he spent a year studying the classical architecture. In the following years he travelled through the countries of Western Europe, where he attended lectures on architecture and learned from the works of the most renowned architects of the time. He visited France, Denmark, Sweden and various German states. He spent a year and a half studying in Paris under the guidance of Jacques-Germain Soufflot and Claude Nicolas Ledoux. On his return, he was hired by Bishop Ignacy Jakub Massalski, for whom he designed and built the episcopal palace in Verkiai, later known after its later owners, the Wittgenstein family. The palace and the surrounding architectural complex, the work on which was commenced by Gucevičius's tutor Knackfus, is currently considered one of the most valuable classicist complexes in Lithuania. In 1789 Gucevičius became a professor of architecture and topography at the Artillery and Engineering Corps' School of Vilnius. In 1794 he also returned to his Alma Mater, where he became a professor of civilian architecture and held the chair in engineering. In 1794, at the outbreak of Kościuszko's Uprising, Gucevičius joined the ranks of the localcivil guard and took part in the Vilnius Uprising against the Russian garrison. He became one of the leaders of the local militia formed out of volunteers. Wounded in a skirmish near Ashmiany, he was demobilised. Following the Partitions of Poland, when Vilnius was annexed by Imperial Russia, the new authorities expelled Gucevičius from the academy for his part in the uprising. However, in 1797 he returned there, this time as a head of the newly founded separate chair of architecture. , as seen in a mid-19th century picture Around that time Gucevičius created the most renowned of his works. First was the new town hall of Vilnius, completed around 1799. He also constructed a similar, yet smaller town hall in Widze near Bratslav. Between 1777 and in 1801 he worked to rebuild the Vilnius Cathedral in the neoclassical style. It is sometimes said that his reconstruction of the cathedral, modelled after a Roman temple, pre-dated the work of Thomas Hamilton and James Playfair, two notable Scottish architects to introduce classicism in the United Kingdom. He is credited with a number of other projects, although their actual authorship is not documented. Among them is the palace of the Tyzenhaus family in Rokiškis, the reconstruction of the castle in Raudonė for its contemporary owners, the Olędzki h. Rawicz family and the manor house in Čiobiškis. He is also thought to have prepared designs of palaces for other notable magnate families of the time, including Radziwiłł, Sapieha, Pac, Chomiński and Scypion, though World War II losses in the preserved archives make the matter difficult to settle definitively. Additionally, he designed several merchant houses in Kretinga and was the author of a topographic map of the western part of the city of Vilnius. He died December 10, 1798, and was buried in the Rasos Cemetery, Vilnius, though knowledge of the exact burial location has been lost. In his last will he dedicated all of his projects to the Polish-Lithuanian Commonwealth, and some of the surviving sketches and designs are currently held in the library of Warsaw University.
