After the civil war of 1948, Guardia and his brothers fled to Nicaragua. Later he moved to Mexico, from whence he returned to Costa Rica in 1958. He was again a member of the Costa Rican government as a deputy from 1958 to 1962 in the administration of Mario Echandi Jiménez. In 1966, he joined with his brother, Rafael Ángel, in forming the National Unification Party, and after his brother's death in 1970, Guardia became the most prominent figure in the party.