Can a Catholic Become a Protestant Pastor?

No, since this would mean leaving the Catholic Church and adhering to the Protestant community with its errors in faith and morals. However, if the priest is a military chaplain of  U.S. armed forces, he is permitted to lead a Protestant service in the absence of a Protestant minister. Of course, this means that he leads prayers and Scripture readings and hymns that are not contrary to Catholic faith as a private act for the benefit of the military personnel who attend, not as a representative of any particular Protestant denomination. Thus, he may not administer their Lord’s Supper, for example. It is also permitted for a Catholic priest or deacon to preach at a Protestant service for a good cause with the permission of the local Catholic bishop, but this would be an exceptional event.