Mathías Olivera Miramontes (born 31 October 1997) is a Uruguayan professional footballer who plays as a left-back or defender for Serie A club Napoli and the Uruguay national team.

After starting his career with few appearance at his home country, he moved to Spanish club Getafe, where he spent five seasons while also being loaned to Albacete in 2018–19. After five years in Spain, he joined Italian club Napoli, winning the Serie A titles in 2022–23 and 2024–25.

Olivera is a former youth international for Uruguay, he made his debut at senior level on January 2022, representing the country at the 2022 FIFA World Cup and 2024 Copa América.

Born in Montevideo, Olivera is a Nacional youth graduate. After progressing through the youth setup, he made his professional debut on 13 February 2016, starting and being booked in a 3–0 away win against River Plate.

Olivera appeared in only one further match for the club, a 2–0 loss at Plaza Colonia on 29 February 2016. In December of that year, he was bought outright by his agent Daniel Fonseca and assigned to Atenas de San Carlos in Segunda División.

In July 2017, Oliveira passed a medical examination at Galatasaray, but eventually did not sign a contract and subsequently returned to Uruguay.

On 14 August 2017, Olivera signed a six-year deal with La Liga club Getafe. He scored his first professional goal on 21 April 2018, netting the game's only in a 1–0 win against Eibar.

On 4 July 2018, Segunda División side Albacete announced the signing of Olivera on a season-long loan deal. He played 15 matches and scored a goal for the club before his loan was cut short by Getafe on 25 January 2019.