Luna was born in Buenos Aires to a family originally from La Rioja Province in 1925. A grandfather had founded the La Rioja chapter of the newly established centrist Radical Civic Union (UCR) in 1892, and an uncle, Pelagio Luna, had been Vice President of Argentina for President Hipólito Yrigoyen, between 1916 and 1919. He enrolled at the University of Buenos Aires and earned a law degree in 1951. He was first published in 1954 with his biographical work "Yrigoyen". Opposed, as most in the UCR were, to the populist President Juan Perón, Luna, after the 1955 overthrow of Perón, was appointed Director of the Ministry of Labor's Employee Benefits Plan in 1956. Luna received his first literary prize in 1957 for his period tale "La fusilación" ("The Firing Squad"); set in the nineteenth century, the work followed the controversial 1956 execution of General Juan José Valle and 27 others. This was followed by a biography of Marcelo Torcuato de Alvear, Yrigoyen's chief rival within the UCR, in 1958.