Luis Mariano Montemayor (born 16 March 1956) is an Argentinian prelate of the Catholic Church who has worked in the diplomatic service of the Holy See since 1991. He has been the Apostolic Nuncio to Colombia since September 2018. He was Apostolic Nuncio to the Democratic Republic of the Congo from 2015 to 2018 and to Senegal, Cape Verde, and Guinea Bissau, as well as Apostolic Delegate to Mauritania from 2008 to 2015. He was the second Argentine to be named a nuncio, after Leonardo Sandri.