 At the seminary in Venegono Inferiore, he served as Professor of Italian (named in October 1931), Professor of Sacred Eloquence (1932–1944), and rector (2 August 1939 – 1953).Professor of Italian language and literature at the Faculties of Education and of Letters and Philosophy of the Catholic University of Sacro Cuore of Milan, 1937–1939.Colombo was raised to the rank of Monsignor on 7 December 1948, and later Rector Major of the Seminaries of Milan on 23 July 1953.