Josefina Aldecoa, née Rodríguez, was born in La Robla, Spain. Her mother and grandmother were teachers. In 1944, she moved to Madrid to enroll in the University of Madrid, from which she received a Ph.D. in pedagogy. Her dissertation was later published as the book El arte del niño (Art of the Child, 1960). While studying, she became connected to a group of writers known as the "Generation of '50." In 1952, she married Ignacio Aldecoa, a member of the group; after his death in 1969, she took his surname as a tribute to him. Her first collection of stories, A ninguna parte (Nowhere), was published in 1962.
Her memoir Los niños de la guerra (Children of War, 1983) chronicled her literary generation.
In 1990, she published her most successful novel, Historia de una maestra (History of a Teacher), the first volume of a trilogy that included Mujeres de negro (Women in Black, 1994) and La fuerza del destino (The Force of Destiny, 1997). She wrote two further autobiographical works, Confesiones de una abuela (Confessions of a Grandmother, 1998) and La distancia (The Distance, 2004). In 1959, she founded a private school in Madrid called Colegio Estilo to provide a secular and creative education, and managed it until her death.