There are three different types of legal marriage ceremonies in Ireland - Civil, Religious and Secular. Civil ceremonies are performed by a registrar who works for the State. Religious ceremonies must be performed by registered solemnisers of established religions, while only registered solemnisers can perform secular ceremonies (such as Humanist). In Northern Ireland the same applies - you must have a registrar for a Civil ceremony or a registered officiant for religious and other weddings where the person who has been registered as an officiant is authorised by the Registrar General