Michał Pius Römer (Lithuanian: Mykolas Römeris; 28 May 1880 – 22 February 1945) was a Polish-Lithuanian lawyer, scientist and politician.

In Paris, he belonged to the organisation "Spójnia", where he headed the group "Lithuania", and was closely related to the Foreign Union of Polish Socialists [pl].

[3] He gave the lecture on cultural-ethnographic situation in Lithuania in Café Voltaire,[3] together with another Lithuanian activist, Tadas Ivanauskas[citation needed].

He wrote works on Poles in Lithuania and Ruthenia and on Lithuanians in the Duchy of Prussia (Litwini w Prusach Książęcych, 1911).

He joined the Society of Friends of Science in Wilno and accompanied Ludwik Krzywicki on his archaeological work in Samogitia.

[3] At the outbreak of World War I, Römer maintained contacts with independence and socialist circles in Warsaw, and distributed leaflets in Lithuania.

In March 1915, he took the Lithuanian politicians Mykolas Sleževičius and Jurgis Šaulys to Warsaw for a meeting with Stanisław Patek.

In August, he submitted an extensive memorandum to the Supreme National Committee entitled Lithuania at War (Litwa wobec wojny).

On September 14, 1915, after a personal conversation with Józef Piłsudski in Kovel, he was assigned to the 1st Legions Infantry Regiment and, under the pseudonym Mateusz Rzymski, took part in the Volhynia campaign as a private.

In August 1917, thanks to the efforts of his Warsawian friends, he was released from the camp and was nominated as a justice of the peace in Kolno in the Kingdom of Poland, and after a year he was transferred to the position of district judge in Łomża.

[4] After the capture of Vilnius by General Lucjan Żeligowski, he went to Kaunas and in a letter to Józef Piłsudski protested against the violation of Lithuania's rights to its capital.

He chose instead to move to Kaunas, which had become the temporary capital of the recently re-established independent Republic of Lithuania.