The question arose in an RCIA session that I taught on whether a Catholic can be the best man in a Protestant wedding. The bride and groom are both Protestant and getting married for the first time. The question stems from the discussion about Catholics participating in non-Catholic worship. I said he could not participate, i.e. receive Communion, but I didn’t have anything solid on why he couldn’t be the witness to the wedding. The bride and groom are not having any other attendants. Can you help?
Assuming that there are no obvious impediments to the marriage (e.g., previous marriage, close blood relationship), a marriage between two baptized Christians would be presumed by the Catholic Church to be valid and sacramental. As such, the Catholic is free to attend the wedding and to participate as an honor attendant. You are indeed correct though that the Catholic may not receive communion at a Protestant wedding.