Nicolás Barrientos (; born 24 April 1987) is a Colombian professional tennis player who specializes in doubles. He reached his highest ATP doubles ranking of world No. 47 on 23 April 2024 and a singles ranking of No. 237 on 21 September 2015. Barrientos has won two ATP Tour doubles titles, including the 2024 Rio Open with Rafael Matos, and 21 titles on the ATP Challenger Tour.
Barrientos made his first appearance on an ATP World Tour in July 2013 when he lost in the first round of 2013 Claro Open Colombia against Ruben Bemelmans.
He made his doubles Major debut at the 2014 US Open partnering compatriot Santiago Giraldo and won his first Major match against Colin Fleming and Ross Hutchins.
At the 2023 Córdoba Open he reached the quarterfinals with Ariel Behar. At the next Golden swing tournament, he reached the final at the 2023 Argentina Open also with Behar where they lost to Bolelli/Fognini.
In 2024, Barrientos began a partnership with Rafael Matos which started to produce good results. At the ATP 250 in Buenos Aires, they reached the semifinals, and in the following ATP 500 tournament in Rio de Janeiro, they won their biggest title, defeating strong pairs such as Krawietz/Putz, Bolelli/Vavassori and Erler/Miedler in the final. As a result he reached the top 50 in the rankings on 4 March 2024.
Partnering Skander Mansouri, he was runner-up at the 2024 Almaty Open, losing to Rithvik Choudary Bollipalli and Arjun Kadhe in the final.
Current until 2025 Hellenic Championship.