A member of the National Liberal Party (PNL), he was Minister of Agriculture (1916–1918), Interior (1918–1919), Labor and Social Protection (1922–1923) and Justice (1923–1926) in successive cabinets of Ion I. C. Brătianu.
[3] Near the end of his term, Mârzescu had to grapple with the logistical difficulties created by Iași‘s becoming the temporary capital of Romania, an event occasioned by military losses and the fall of Bucharest in World War I.
In On December 13, 1918, a typesetters' protest in front of the National Theatre in the capital clashed with Vânători de munte troops, leaving six dead and numerous injured.
In that capacity, he pushed through a number of laws; among the subjects these dealt with were acquisition and loss of Romanian citizenship; combating offenses against public order; simplifying legal procedures for speedier trials; reorganizing courts, particularly in the territories acquired at the end of the war; restricting firearm ownership; simplifying procedures for heirs of those killed in action during the war; reforming the High Court of Cassation and Justice; and setting up a Legislative Council—the last two in pursuance of the new 1923 Constitution.
[5] The citizenship law allowed for the naturalization of Jews, which made Mârzescu a leading target for assassination by far right activist Corneliu Zelea Codreanu and his allies.
[8] The law, which effectively reduced the Communist group to a base of committed activists, was advocated by all the major political forces, ever since the party had publicized its pro-Comintern platform.