Mario Pezzi was born in Gottolengo (Brescia, Italy), on September 19, 1942, and is the third of five brothers. He entered the seminary of the Comboni Missionaries at 10 years old. After the novitiate, he was sent by the Superiors to Rome to the International Scholasticate and studied Theology at the Pontifical Urban University. He received the priestly ordination on March 19, 1969 and began his PhD in Dogmatic Theology at the Pontifical Gregorian University with Professor Father Zoltan Alszeghy.
In that same year, he met Kiko and Carmen, initiators of the Neocatechumenal Way, and attended the last catechesis they did in the parish of the Natività of Rome. In January of 1970, he received the catechesis of the Way in the parish of San Giovanni di Dio, in which he was ministering and entered in the first neocatechumenal community of this parish. Seeing in the Way a hope for the catechumenate in the missions in Africa, especially after the tragic experience of the massacres among Christians in Burundi, he obtained permission from his superiors to make an experience as an itinerant of the Way in view of the mission in Africa. In September of 1970, he interrupted his doctorate studies and was sent by Kiko and Carmen to start the Way in two parishes of the diocese of Brescia and Milan, and in January of 1971 to the parish of San Leone in Catania.
In June of 1971, he was invited by Kiko and Carmen to replace D. Francesco Cuppini, the presbyter who had accompanied them since 1968, thus forming part of the team in the periods in which they evangelized in Italy, especially in Rome, and in Florence and Ivrea. In the periods in which Kiko and Carmen were in Spain, accompanied by Father Jesús Blázquez as a presbyter, Father Mario was sent to evangelize Lombardy and then to Portugal. In December of 1981, with a letter from the Superior General of the Combonians, was sent as an itinerant Comboni Father to start the Way in Khartoum (Sudan), heart of the Comboni missions, and then in March of 1982, to Kampala (Uganda). Since then he made numerous trips to Africa, visiting several bishops in Kenya, and families in mission of the Way in Ivory Coast, Cameroon, Zambia, and Redemptoris Seminaries Mater de Kitwe (Zambia), Douala (Cameroon), Dar es Salaam (Tanzania), Goma (Congo), and Morondava (Madagascar). He also visited several bishops first in Angola and then in Mozambique to open the Way. He was in Bangui (Central African Republic) and Bujumbura (Burundi).
Since 1982 he had been called to join the responsible team of the Neocatecumenal Way with Kiko and Carmen, full time, accompanying them in their work of relationships with the Pope, the Holy See, the bishops, in the steps of the Way, in the convivences of the itinerants, and in international travel and meetings, until present day. In 1992, the New Comboni superiors invited him to join the Institute again or incardinate in the Diocese of Rome. The Cardinal Vicar of Rome Monsignor Camilo Ruini received him as a itinerant catechist priest of the Diocese of Rome.
With the approval of the Statutes in 2002 ad experimentum, and in 2008 definitively, he has been appointed by the Holy See presbyter of the International Team, together with Kiko and Carmen (before she passed away).