Elected mayor of Iași in 1914, he served for two years. 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. He worked to ensure an adequate food supply and sought to house refugees, whose influx swelled the city’s population to around 400,000. Personalities at the Iași, Capitală de Război site In November 1916, he became vice president of the Chamber of Deputies.Popescu and Prelipceanu, pp.35–6 From December 1916 to January 1918, he was agriculture minister in the cabinet of Ion I. C. Brătianu, whom he supported consistently.Popescu and Prelipceanu, p.36 This was a coalition government between the PNL and the Conservative-Democratic Party. Seeing food production as essential to the war effort, he and those around him took special measures: creating agricultural advisers with enhanced powers and county-level military structures; directing agronomists to draw up harvest plans at the commune and county level; ordering the land owned by mobilized troops to be farmed without pay by those left behind; buying up with state funds all excess grain in order to combat speculation; ordering all agricultural laborers, regardless of age or sex, to be requisitioned for farm work.
