Tonini furthered his studies at the Pontifical Lateran University in Rome, obtaining his degrees in civil and canon law, from 1939 to 1943.

From 1943 to 1969, he did pastoral work in the Diocese of Piacenza and for many years he was the pastor of parish of Salsomaggiore, as well as serving as ecclesiastical assistant of the Federation of Catholic Italian University Students, director of the weekly Il nuovo giornale, and professor and rector at its seminary.

After reaching the mandatory retirement age of 75, he resigned the governance of his see on 27 October 1990, following fourteen years of service.

Tonini preached the Lenten spiritual exercises to the Pope and members of the Roman Curia in February 1991 on the theme of "the Church of hope for today".

Pope John Paul II created him Cardinal-Priest of Santissimo Redentore a Valmelaina in the consistory of 26 November 1994.