His father, Pieter C. Swart, was editor in chief of the Nieuwe Rotterdamsche Courant; his mother was J. G. Gratama.
Swart was educated in The Hague and at the University of Leiden, where he took the candidature in Law before transferring to History.
In 1966 he succeeded Ernst Kossmann as Professor of Dutch History and Institutions at University College London, holding the chair until his retirement in 1983.
[1] Swart was elected a correspondent of the Royal Netherlands Academy of Arts and Sciences in 1967.
[2] Swart married Ineke de Leng in 1950 and had four children Sonia (1952), Peter (1954), Stephanie (1957) and Philip (1961).