Q. 1. If a priest has been laicized, can he still return to the priesthood?
A. 1. According to the Canon Law of the Catholic Church, a priest is a priest for life.
Canon Law # 1582 "As in the case of Baptism and Confirmation this share in Christ's office is granted once for all. the sacrament of Holy Orders, like the other two, confers an indelible spiritual character and cannot be repeated or conferred temporarily."
Canon Law # 1583 "It is true that someone validly ordained can, for a just reason, be discharged from the obligations and functions linked to ordination, or can be forbidden to exercise them; but he cannot become a layman again in the strict sense, because the character imprinted by ordination is for ever. The vocation and mission received on the day of his ordination mark him permanently."
Accordingly, a priest who has voluntarily left the priesthood, may be reinstated to the priesthood, providing there are no Canon Law obstacles. This excludes the priests who have been removed from the priesthood by the Vatican because of public scandal.
When a priest is reinstated into the priesthood within his diocese or a religious institute, he does not have to be ordained again because once a priest, always a priest.