He was born in 1888 in Piatra Neamț, the son of Vasile and Andromaca Manoliu, both civil servants, originally from the Ceahlău region. After graduating from Petru Rareș High School in his native city, he attended the Infantry School for Officers in Bucharest, graduating in 1909 with the rank of second lieutenant. Promoted to lieutenant in 1912, he served in 1913 in the Second Balkan War. After Romania entered World War I in August 1916 on the side of the Allies, Manoliu fought in the Romanian Campaign of 1916, commanding an infantry battalion. He fought in the Battle of Transylvania and then at First Battle of Oituz. He was promoted to captain in May 1917 and, after distinguishing himself at the Third Battle of Oituz, to major in September 1917.