Mieres began playing rugby at a young age for Lobos, the only rugby team in his birthplace of Punta del Este, Uruguay. Due to his great speed and footwork, as well as a remarkable skill for tackling he was selected to play for the national youth teams throughout every category.
In 2010, he received his first full cap for the first team of Los Teros and then went on to alternate between Los Teros XV's team and the 7's team, depending on each's calendar.
In 2014 he made his professional debut for Rugby Club Valpolicella of Verona, Italy of the second tier of the Italian Rugby Union championship. This came after outstanding performances in several test matches and the 2015 Rugby World Cup qualifying.
He has played at the 2011 Rugby World Cup qualifying and at the 2015 Rugby World Cup qualifying, where Los Teros achieved the feat of beating Russia in the playoffs for the last place at the World Cup.
Mieres ranked third in the Most Offloads Made ranking of the 2015 Rugby World Cup during the group stage for having made seven offloads, the same as world renowned off-loader Sonny Bill Williams of the New Zealand All Blacks
In November 2015, Mieres was tested on a week trial on Coventry Rugby Club, till he finally signed a short contract with the team.
The player returned to Lobos in early 2016.
In 2019, he signed with Canadian club Toronto Arrows ahead of the Major League Rugby season. Since then, he has played 26 matches and scored 9 tries across 3 seasons. (2020-2022)
Ahead of the Rugby World Cup 2023, Mieres has been named in the squad for Uruguay.
|2018 - present|
|2023 - present|
|2019 - 2023|