 Since 1975, Delpini taught the Italian language in the minor seminary of his native archdiocese and in 1989 he was named as the rector of the minor seminary.In 1993, he was named as the dean of the seminary of Venegono Inferiore and in 2000 he became the rector of all seminaries of the Milan archdiocese.In 2006, Cardinal Dionigi Tettamanzi placed him in charge of one of the archdiocesan zones.