Note: The short title of "Attending a Protestant marriage" means more precisely "Attending a wedding that is taking place in a Protestant church building."
Q. 1. As a Catholic, am I allowed to attend a Protestant marriage/wedding?
A. 1. There is no one answer to your question because it depends on the circumstances. Allow me to explain:
A. In a situation where you are permitted to attend a Protestant marriage, under no circumstances are you permitted to receive communion at their celebration. If you were to do so, you would be affirming that receiving Holy Communion in Protestant churches is equal to receiving the Holy Eucharist in the Catholic Church, which it is not.
One reason to support this is that in the Catholic Church, the Holy Eucharist is the Real Presence of Jesus from the moment of the Consecration until such time as it is consumed. Most Protestant churches (excluding some of them such as the Anglicans and the Lutherans), do not believe in the Real Presence of Jesus in the Consecrated Host. To them, communion is symbolic of the Last Supper.
Secondly, when you attend a Protestant wedding in a denomination that does not have valid ordinations, communion, even if the denomination officially believes it to be the Real Presence, is only bread and wine. In other words, if you went to an Anglican or Lutheran wedding, even though they believe in the Real Presence, their communion is only bread and wine because their ministers are not validly ordained.
According to the 1983 Code of Canon Law # 844.2, the only exception regarding a Catholic receiving the Sacraments from a non-Catholic minister is when it is impossible for the Catholic to receive the Sacraments from a Catholic priest and the non-Catholic priest is one “in whose Churches these sacraments are valid.” This means that, unless the non-Catholic institution teaches that the “bread and wine” becomes the body and blood of Christ (such as the Eastern Orthodox or Polish National Catholic), the Catholic can never receive communion from a minister or priest who officially represents it.
A Catholic not having access to his or her own Catholic priest is a very rare occurrence, but it could happen, and you could even find a non-Catholic institution with valid sacraments. BUT in such a situation, you as a Catholic are required first to ask permission to receive from the officiating non-Catholic priest. This would mean that you would have to explain why you are a Catholic who cannot receive from a Catholic priest.
NOTE: Eastern Orthodox priests who value their orthodox reputations never grant permission for communion to a committed Catholic, no matter what his or her circumstances happen to be!
If he or she (i) knows that taking communion from a Protestant minister is a serious offense against God, (ii) has reflected sufficiently on the degree of this offensiveness, (iii) and freely chose to do it anyway, he or she has then committed a mortal sin.
B. If the Protestant marriage is between two Protestants who are relatives or your friends, (neither party being ex-Catholic or divorced), and you have been invited, you may attend. Some attend Protestant services in the spirit of ecumenism. Others do so to learn about the Protestant beliefs and liturgy. Whatever the reason, you still cannot receive communion in their church.
C. If the Protestant marriage involves a Catholic and a Protestant, the Catholic having received a dispensation from his/her Bishop, you can attend. If a dispensation has not been obtained from the Bishop, you should avoid such a wedding, even if the Catholic is your mother, your father, a grandparent, your brother or sister, an aunt or uncle, a son or a daughter. Such a wedding means that the Catholic bride or groom is ignorant, or is renouncing the Catholic faith and belief in a Sacramental Marriage, or at least violating his or her conscience. If someone informs them (the earlier the better) about the truth in the time leading up to this wedding, and they persist in their plans to get married in this way, they are seriously offending God. You must not attend under such circumstances.
By attending such a marriage, you are giving your seal of approval to the Catholic who is getting married, silently saying that what he is about to do is okay. By attending such a marriage, you become guilty of his sin. One can sin many ways as is seen below:
(1) By counsel (if you advised him to go ahead with the marriage);
(2) By command;
(3) By consent (if you agreed it is alright);
(4) By provocation;
(5) By praise or flattery;
(6) By concealment;
(7) By partaking (if you attended);
(8) By silence (if you said nothing about the rejection of his faith);
(9) By defense of the ill done (by defending his action).
D. Since April, 2010, the Catholic Church treats all ex-Catholics as Catholics when it comes to marriage, and so attendance is immoral, because ex-Catholics cannot get a dispensastion from their Catholic bishop without returning to the Catholic Faith..
Between 1968 and 2010, only when it came to marriages, Catholic law treated never-married ex-Catholics who joined another denomination before they married a life-long Protestant as life-long Protestant as if they were also life-long Protestants. Such marriages could have been attended as valid.
A divorced Catholic who obtained a Catholic annulment for each of his or her previous legal marriages is treated as a Catholic who has never been married in God's sight. This is because God's laws are what cause a marriage in God's sight, not human laws. So you may attend his or her wedding, as long as a Catholic priest performs it or it has the bishop's permission. [Note: This full-page response has been carefully reviewed by a Catholic priest in good standing with his bishop.]