Margarita del Carmen Brannon Vega was born in El Salvador on 20 December 1899 to Patrick (Patricio) Brannon, an Irish engineer, and a Salvadoran, Manuela Vega. From her father she acquired a liberal education and a taste for poetry and literature, as well as sympathy for socialism and theosophy. In her early years she was educated at home and later attended the Colegio de La Asunción, run by Catholic French nuns in the western city of Santa Ana. She was a classmate of the mother of another well-known writer, Claribel Alegría. Both Lars and Alegría have been recognized as the most prominent Salvadoran female poets.

Brannon wrote her first book, Tristes mirajes (Sad Mirages), in 1915-1916, when she was sixteen years old. Although there are no copies extant, in the May 1921 issue of Repertorio Americano (American Repertoire) the Nicaraguan avant-garde poet Salomón...