Römer was born in Lithuania into a Polonized noble family of Baltic-German (Livonian) origin. He was one of szlachta members loyal to the heritage of the Grand Duchy of Lithuania, referred to as Krajowcy. His father was Micha? Kazimierz Römer and mother was Konstancja Tukaa.
He attended the Law School in Sankt-Peterburg (1893-1901) and later studied history in Kraków (1901-1902), after that he moved to Paris to study in École des sciences politiques (1902-1905). He gave the first lecture on Lithuania in Paris in 1905, together with another Lithuanian activist, Tadas Ivanauskas. In 1908 he wrote Lithuania: Study of national revival (Litwa: studium odrodzenia narodowego).
Later Römer became a member of Pi?sudski's Polish legions, but broke with the Polish side. In 1920, he declined an offer to become the prime minister of the Republic of Central Lithuania. He chose instead to move to Kaunas, which had become the temporary capital of the recently re-established independent Republic of Lithuania.
He was a notable figure in the interwar period, and was a member of the Lithuanian Supreme Tribunal (1921-1928) and the State Council of Lithuania (1928-1931). He was a professor at the University of Lithuania/Vytautas Magnus University (1922-1940), Vilnius University (1940-1945), and the rector of the University of Lithuania for three terms (1927-1928, 1933-36 and 1936-1939). As an international lawyer, in 1932 he represented Lithuania at the Permanent Court of International Justice regarding the Klaip?da Directorate. The court found in Lithuania's favor that Otto Böttcher had violated the Statute of the Klaip?da Region.
Römer wrote important works on Lithuanian history and on law, such as the 1908 book Lietuva. Studija apie lietuvi? tautos atgimim? and the 1928 book Die Verfassungsreform Litauens im Jahre 1928. He is considered to be one of the most prominent Lithuanian jurists, the progenitor, first lector and one of the most prominent authors of interwar Lithuanian constitutional law. While most of his writings on Lithuanian law were written in Lithuanian and his signature on Lithuanian documents and letters was Mykolas Römeris, (sometimes also credited as Mykolas R?meris or Mykolas Riomeris), he continued to write his diary in Polish and use the original German form of his name (Michael von Römer) for his law writings in German.
The Law University of Lithuania in Vilnius was renamed to the Mykolas Romeris University in 2004.