*Club domestic league appearances and goals, correct as of 13 September 2024 ‡ National team caps and goals, correct as of 19:45, 11 October 2016 (UTC)
He began his career in the youth academy of Standard Liège. De Sart went on to sign his first professional contract with the club's senior team in 2013, making his debut in that same year. In 2016, he signed for Middlesbrough, who would go on to achieve promotion to the Premier League that same season. He rarely played at the club, and went on loan to Derby County for more first-team experience. Following his parent club's relegation, he was sent on loan to Zulte Waregem.
On 22 August 2013, De Sart made his debut in the UEFA Europa League against Belarusian FC Minsk in a 2–0 away win. He played the full game. He's a youth exponent from the club. He is the son of Jean-François De Sart who has been a board member of Standard Liège, and the elder brother of Alexis De Sart who previously played for Standard Liège.[citation needed]
He made his league debut at 25 August 2013 against R.A.E.C. Mons in a 2–0 away win, coming off the bench in the first half for an injured Yoni Buyens. After 83 minutes he was sent off with a second yellow card.[2] At 24 November 2013, he scored the only goal against R.A.E.C. Mons.[citation needed]
Middlesbrough
On 1 February 2016, it was confirmed that De Sart had joined English club Middlesbrough of the Championship side on a three-and-a-half-year contract for an undisclosed fee.[3]
On 5 January 2017, it was confirmed that De Sart would be moving to Derby County on loan for the remainder of the season.[4] He scored his first goal for Derby in a 4–3 loss to Cardiff City on 14 February 2017.[5]