Sebastián Coates Nion (Spanish pronunciation: [seβasˈtjaŋ koˈates ˈnjon]; born 7 October 1990) is a Uruguayan professional footballer who plays as a centre-back for Uruguayan club Nacional.

Having begun his career at Nacional, where he was a regular from his debut in 2009, Coates joined Liverpool in 2011. He spent time out on loan, back at Nacional, and at Sunderland, and then joined the latter permanently in 2015. In January 2016, he moved to Sporting, initially on loan before signing permanently in February 2017. Following his move, Coates became an important member of the Sporting squad, captaining the side, and leading the club to a number of trophies, including the club's first league title in 19 years during the 2020–21 season.

Coates made his international debut at the 2011 Copa América, and was voted Young Player of the Tournament after Uruguay won the final. He also represented the country at the 2012 Olympics, the FIFA World Cup in 2014, 2018 and 2022, and the Copa América in 2015 and 2019.

Coates was born in Montevideo. On his paternal side, he is of Scottish ancestry, although his family does not speak English.

Coates joined Nacional at 11, and worked his way up through the age groups, appearing as captain at every level. In 2009, aged 18, he signed a contract and began playing for the first team. His first appearance came against Bella Vista, a performance for which he was named man of the match by Uruguay's El País. He subsequently started every game for Nacional, notwithstanding suspension and national duty.

In August 2011, Coates was the subject of substantial interest from Premier League club Liverpool. He was given permission to have a medical at Melwood ahead of his proposed move on 26 August, and the following day watched Liverpool's match against Bolton Wanderers. On 30 August, after receiving a work permit, Liverpool announced that they had signed Coates on "a long-term contract" for an undisclosed fee, reported to be around £7 million.

On 18 September, Coates made his debut for Liverpool against Tottenham Hotspur, replacing the injured Daniel Agger in the 27th minute, in a 4–0 defeat. Coates went on to make his first start for the club on 21 September against Brighton & Hove Albion in the League Cup. Liverpool won the match 2–1 and Coates started the next match in this competition against Stoke City which Liverpool also won 2–1. Liverpool progressed through all stages to win the tournament resulting in Coates winning his first medal as a Liverpool player. On 21 March 2012, he scored his first goal for Liverpool against Queens Park Rangers, with a scissor kick from the edge of the box in the 3–2 loss at Loftus Road.

Coates suffered a knee injury playing for Uruguay in a friendly match against Japan in August 2013. The injury sidelined the player for much of the 2013–14 season. The second half of the season saw Coates return to Nacional on loan, helping him to secure a place in Uruguay's World Cup team.