A Fulbright scholar (1960–1961), he obtained his professorship in 1965 and was Professor Emeritus at University of California, San Diego.
A disciple of both Jaume Vicens i Vives and the prominent French historian Pierre Vilar, Jackson was a regular collaborator of the Spanish daily El PaÃs for many years.
In 1966 he was awarded the American Historical Association's Herbert Baxter Adams Prize, and in 2002, Spain's prestigious Nebrija Prize from the University of Salamanca.