Following his graduation Sullo worked as a history and philosophy teacher in high schools from 1944 to 1946. Sullo was named as the national leader of a leftist faction (Italian: Sinistra di Base) in the party.{{cite thesis|author=Robert Raymond Gilsdorf|title=Factionalism in the Italian Christian Democracy Party, 1958-1963|url=https://www.proquest.com/docview/302459437|degree=PhD Sullo served as state secretary in three successive cabinets between 1957 and 1960. He was appointed minister of transport on 25 March 1960 to the
cabinet of
Fernando Tambroni. Sullo resigned from the post on 11 April 1960.{{cite news|author=Mario Macchioni|title=Il democristiano meno democristiano di tutti|access-date=22 August 2022|work=
Il Post In December 1968 Sullo was appointed minister of education in the cabinet of
Mariano Rumor. Sullo resigned from office in February 1969. From February 1972 to July 1973 he served in the
first and
second cabinets of Giulio Andreotti as state minister without portfolio. In March 1974 Sullo resigned from the Christian Democracy and joined the
Italian Social Democratic Party in June that year. However, he was elected to the Parliament in 1983 on the list of the Christian Democracy where he served until 1987. ==Personal life and death==