Sebastien Thill plays for Moldovan club Sheriff Tiraspol on loan from Progres Niederkorn and the Luxembourg national football team. The 27-year-old is the older brother of fellow Luxembourg internationals Olivier Thill and Vincent Thill. From 2009 to 2012, Sebastien scored 9 goals in 46 league appearances for CS Petange of the Luxembourg National Division. He moved to FC Progrès Niederkorn in 2013, and made his European club competition debut two years later during the first qualifying round of the 2015–16 UEFA Europa League.

In 2017, Sebastien scored the winning goal in Progres Niederkorn’s 2–1 aggregate win against Scottish side Rangers FC in the UEFA Europa League first qualifying round.

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Sebastien joined Russian club FC Tambov on a season-long loan in 2020 before joining Moldovan club Sheriff Tiraspol on a year-and-a-half loan the next year. Thill made his senior international debut for Luxembourg on 5 September 2015 in a UEFA Euro 2016 qualifying match against Macedonia, in which he also scored his first international goal.

His long range goal against Real Madrid helped Sheriff secure a historic 2–1 victory in their first UEFA Champions League campaign on September 28. The Moldovan club held on to their lead after Jasurbek Yakshiboev scored the first goal for them until Karim Benzema pulled off a 65th-minute spot-kick.

However, Sheriff struck again, when Sebastien scored in the 89th minute to settle the game in favour of his team.

Sheriff beat Shakhtar Donetsk 2-0 in its opener at home, while Madrid won 1-0 at Inter.

Sheriff is the first club from the Moldovan league to qualify for the group stage of the Champions League, although it is based in the breakaway region of Transnistria, a self-proclaimed independent nation that is not recognized by any United Nations member state.