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.

After earning a degree in canon law, he entered the diplomatic service of the Holy See on 1 July 1991 and worked in Ethiopia, Brazil, and Thailand.

[3] He received his episcopal consecration on 6 August 2008 in Buenos Aires from Archbishop Dominique Mamberti.

[1] On 22 June 2015, Pope Francis named him Apostolic Nuncio to the Democratic Republic of the Congo.

[7] He stated in 2024 that the Church in Ireland would undergo a reorganisation, "In due time, and following careful assessment and consultation, the present Dioceses of Tuam and Killala on the one hand, and Elphin and Achonry on the other, may be governed by one Bishop in each case, just as the Dioceses of Galway and Clonfert are today governed by one Bishop.