A member of the Christian Democrat Party of Chile, Pareto served as a deputy, and in that role, he became the President of the Chamber of Deputies of Chile from 23 May 1973 until the coup d'état on 11 September of that year, and between March 2001 and March 2002. He also served as the Intendant of the Santiago Metropolitan Region during the presidency of Patricio Aylwin, the first of the Chilean transition to democracy (1990–1994).