Pareja was born in Guayaquil in 1908, the son of Fernando Pareja y Pareja (1862-1919) and of Amalia Diez-Canseco y Coloma (1865–1945), daughter of the former Peruvian President Francisco Diez Canseco y Corbacho and his wife. Pareja had to support his family from the age of 14. He read at night and assisted as a gate listener at the Colegio Vicente Rocafuerte, which was co-ed until 1937. He would monitor student conversations to ensure proper decorum.

Pareja completed his early education in his hometown: primary school at the Colegio San Luis Gonzaga of the Christian Brothers. In 1927 Pareja and Jorge Pérez Concha founded the magazine Voluntad in collaboration with Leopoldo Benites Vinueza, but they published only six issues.

In 1930, Pareja embarked on an adventure in the United States. As a result of the Great Depression, he worked on the New York City docks for a year (his later novel El Muelle (The Pier, 1933) reflects these experiences).

In 1934 he married Mercedes Cucalón Concha, a second cousin and niece of Carlos Concha Torres and his wife. They had three children together: Cecilia, Jorge and Francisco.

In 1944 Pareja was appointed as Ecuador’s chargé d’affaires in Mexico. In 1945 he became a special representative for the United Nations Relief and Rehabilitation Administration (UNRRA) in Washington D.C.. He later served in Montevideo and Buenos Aires, coordinating for the governments of México, Central American nations, Argentina, Uruguay, and Paraguay.

Pareja’s cycle of narrative fiction was marked by realism and a strong connection with the history of his country (El muelle [“The Pier”], 1933; Hombres sin tiempo [“Men Without Time”], 1941; Las tres ratas [The Three Rats], 1944). Having established a reputation as a writer both inside and outside of Ecuador, in 1944 he published an important biographical novel, The Barbaric Bonfire, about the actions and historical circumstances surrounding the life and death of General Eloy Alfaro.

Between August 1979 and July 1980, during the government of President Jaime Roldós Aguilera, Pareja was appointed to the post of Minister of Foreign Affairs. During the rule of Roldós’s successor, President Osvaldo Hurtado, he served as Permanent Delegate to UNESCO and Ambassador to Paris (1983–84).

After retirement, Pareja dedicated his time to historical research. He died in Quito on 1 May 1993.