Some have asked me about the validity of Orthodox priests within the Catholic Church and if they are accepted as “legitimate”. The following quote is from EWTN’s website where an Orthodox Hieromonk asked about the validity of his priesthood should he come into communion with Rome.
An Eastern Orthodox priest who becomes Catholic is not re-ordained. Nor must he go through seminary training again. He can continue serving as a priest in the Catholic Church, at the discretion of his Catholic bishop.
…the Catholic Church views the Orthodox Churches as true Churches with apostolic succession and a valid priesthood. Dominus Iesus is an authoritative document that gives the official position on this matter.
Any Eastern Orthodox Christian who becomes Catholic must retain his own Byzantine rite, and therefore automatically becomes Byzantine Catholic. This applies to clerics as well as to laity. Thus, an Eastern Orthodox priest who becomes Catholic automatically becomes a Byzantine Catholic priest. As to whether or not he may enter a religious order or be diocesan, this is up to the discretion of the bishop who receives him into the Catholic Church.
An Eastern Orthodox priest who desires to become Catholic should contact a Byzantine Catholic bishop to discuss possible arrangements. There are several different kinds of Byzantine Catholics in the United States, including Melkite, Ukrainian, Romanian, and Ruthenian Byzantine Catholics. Each group has their own bishops. Each bishop may handle these cases differently. Ultimately it is the bishop who makes the final decisions in such matters. (Link.)
The following quote is taken from ETWN’s website where someone asked about coming into communion with Rome.
Canon 896 specifies that for those adult Christians (beyond 14 years) “who ask of their own accord to enter into full communion with the Catholic Church, whether as individuals or as groups, no burden is to be imposed beyond what is necessary.”
Canon 897 indicates that the Christian may be received “With only the profession of faith after a doctrinal and spiritual preparation that is suited to the person’s condition.”
With respect to individual laypersons the right to receive usually pertains to the pastor although in some cases particular law might reserve this admission to a higher authority (cf. Canon 898.3).
Canon 35, however, is important because it specifies that baptized non-Catholics entering into full communion “should retain their own rite and should observe it everywhere in the world as far as humanly possible. Thus they are to be ascribed to the Church ‘sui iuris’ of the same rite.”
When the person wishes not only to become Catholic but to change to the Latin rite, the same canon recognizes the right to approach the Holy See (the Congregation for Eastern Churches) in special cases.
Therefore, in the case at hand, the simplest thing to do is to approach the Eastern eparchy most closely resembling his original rite in order to be admitted into the Catholic Church in accordance with the dispositions of the pastor.
Once admitted, he should continue to practice the faith in the corresponding Eastern rite. But he may also freely practice in the Latin rite for a just cause, for example, if there were no churches of his own rite within a reasonable distance.
In order to formally switch rites, he would need to recur to the Holy See as mentioned above. (Link.)
Nec plus, nec minus, nec aliter.