 The pair had no children of their own, but had an adopted daughter Marytė Sleževičiūtė-Mackevičienė.Marytė married Mečislovas Mackevičius, who would later serve as the minister of justice on the Provisional Government of Lithuania in 1941.Mykolas Sleževičius' brother Kazys Sleževičius was a prominent geophysicist in Lithuania, Head of the Department of
Geophysics and Meteorology at the Lithuanian University (now Vytautas Magnus University), later at the Vilnius University.