In 1947 Lombardini began his career as a
research assistant and following the completion of his PhD he started to give courses in
political economy at his alma mater, Università Cattolica. From 1954 to 1958 he also taught at the Faculty of Law of the
University of Modena. In 1956 he joined the
University of Bari as the chair of the department of political economy. In 1957 Lambordini became a full professor.{{cite web|author=Alberto Quadrio Curzio|title=Siro Lombardini, un anno dopo|work=Cattolica News From 1958 to 1968 Lombardini was the director of the Economic and Social Research Institute in
Turin. He later joined the Christian Democrats and became a member of the
Italian Senate for the seventh legislature (1976–79). In 1979 he was appointed minister of state holdings to the
cabinet led by
Prime Minister Francesco Cossiga. Lombardini was in office between 5 August 1979 and 4 April 1980. During his tenure he was accused of involving in the Eni bribe scandal. Following his retirement from politics he was named the president of the Banca Popolare di Novara on 26 September 1995. He merged the institution with the
Banca Popolare di Verona which created the current
Banco Popolare. ==Personal life and death==