He has taught at Columbia since 1969, except for a year at the University of Pennsylvania (1976–1977)
Somerville did his doctoral work under Stephan Kuttner at Yale University. He has published widely on the high medieval history of the papacy and of canon law. He is internationally recognized as an authority on medieval church councils.
With the publication of his 2011 book, he has published completely all the sources relating to the councils of Pope Urban World War II In 2012, the Catholic University of America Press published a festschrift in his honor Canon law, religion, and politics: Liber amicorum Robert Somerville, edited by his former students Uta-Renate Blumenthal and Anders Winroth, and also by Peter Landau.
He is a corresponding member of the Monumenta Germaniae Historica, Munich, and of the Bavarian Academy of Sciences.