During his time with Juventus, De Agostini achieved his first senior international cap in a 0–0 draw against Norway on 28 May 1987. With Italy, he participated in Euro '88, scoring against Denmark, as Italy went on to reach the semi-finals. He also took part in Italy's footballing campaign at the 1988 Summer Olympics, where they managed a fourth-place finish after reaching the semi-finals yet again. He was also a substitute member of Italy's squad at the 1990 World Cup on home soil, where the team also managed to reach the semi-finals, only to suffer a penalty-shootout defeat to defending champions Argentina, following a 1–1 draw after extra-time; despite the loss, De Agostini was able to net his penalty in the shoot-out. Italy subsequently went on to capture the bronze medal following a 2–1 victory over England in the third-place match. Under manager Azeglio Vicini, he was also often deployed as a wide midfielder or as a wing-back, in addition to his more regular full-back role. Unfortunately, his time with Juventus also included his last game for the Italian national team on September 25, 1991, in a 2–1 home loss to Bulgaria, during Italy's qualifying campaign for Euro 1992. In total he made 36 appearances for Italy, scoring 4 goals.