2018: Davis Cup debut

Vliegen made his debut with the Belgium Davis Cup team in 2018. In the quarterfinals against the United States, he and fellow Belgian Sander Gillé lost against Ryan Harrison and Jack Sock.^[5]

2019: Grand Slam debut and first quarterfinal, Three ATP doubles titles

In 2019 he and Gillé managed to pull off a surprise win over Brazil's Marcelo Melo and Bruno Soares in the Belgium-Brazil Davis cup tie contributing to Belgium qualifying for the 2019 Davis Cup Finals held in November.^[6]

Vliegen made his Grand Slam debut in the 2019 French Open. Partnering Mikhail Kukushkin from Kazakhstan he managed to reach the quarterfinals.^[4] At Wimbledon 2019, Vliegen made his debut in a mixed doubles event, and reached the third round with Zheng Saisai from China.^[7]

Vliegen won his first ATP Tour doubles title at the 2019 Swedish Open with fellow Belgian Sander Gillé.^[8] One week later, again partnering with Gillé, he also won the title at the Swiss Open.^[9] The duo continued their winning streak by reaching the final of the Austrian Open, losing to Philipp Oswald and Filip Polášek.^[10] Two months later, Vliegen and Gillé picked up their third title of 2019 at the Zhuhai Championships.^[2]

2020–2021: Two titles, Second Major quarterfinal, first Masters semifinal, Olympics & top 30 debut

Vliegen won two more titles with his partner Sander Gillé at the 2020 Astana Open and at the 2021 Singapore Open. They also reached the quarterfinals at the 2020 US Open (tennis) losing to the eventual runners-up Mektic/Koolhof, their best showing at the Grand Slam thus far. The pair made their first Masters 1000 semifinal at the 2021 Mutua Madrid Open losing to the 2nd seeded pair of Pavic/Mektic. As a result, Vliegen reached a career-high of No. 31 on 10 May 2021.

2022: First Grand Slam mixed doubles final

At the 2022 French Open, Vliegen and Gillé caused an upset by eliminating the defending champions and home favorites Pierre Hugues Herbert and Nicolas Mahut in three tight sets without dropping one service game. In the second round they saw off the Australian pairing of Luke Saville and Jordan Thompson before falling to the unseeded pairing of Rafael Matos and David Vega Hernández in a third super match tie-break.

He also entered the mixed doubles event for the first time, partnering Norwegian Ulrikke Eikeri. In the first round they won against the Kazakh pairing of Anna Danilina and Andrey Golubev in three sets. In the second round they progressed past the home team of Clara Burel and Hugo Gaston in straight sets. In the third round they faced 2021 Wimbledon champions Desirae Krawczyk and Neal Skupski and lost the first set comprehensively before bouncing back to win the second set in the tie-break and the third set match tie-break.^[11] Their semifinal followed a similar pattern, this time against 2018 Wimbledon champion Nicole Melichar and twice French Open Men's doubles champion Kevin Krawietz, with them again bouncing back from a poor first set to win the second in the tie-break and the third set match tie-break to reach their first Grand Slam final. They lost in the final to Ena Shibahara and Wesley Koolhof.^[12][13] This made Vliegen the first Belgian man to reach the final of a mixed doubles event of a Grand Slam tournament.

2023: First Grand Slam men's doubles final, second mixed doubles final, top 20 debut

At the 2023 French Open, Vliegen having never get passed the quarterfinals at this Major, partnering Gillé as an unseeded pair, they reached their first Major semifinal defeating fourth seeds Croatians Nikola Mektić/Mate Pavić, Roman Jebavý/Luis David Martínez, ninth seeds Santiago González/Édouard Roger-Vasselin, 14th seed Argentines Andrés Molteni/Máximo González^[14] and 12th seeds Andreas Mies/Matwé Middelkoop.^[15][16] In the final they lost to Ivan Dodig and Austin Krajicek in straight sets.^[17] At Wimbledon, he and Gillé lost in the third round of the men's doubles event, while Vliegen paired with Xu Yifan in mixed doubles to reach his second career final. This made him the first Belgian man in a Wimbledon mixed doubles final. He made his top 20 debut on 7 August 2023 at world No. 17.

Grand slam finals

Doubles: 1 (runner-up)

Result	Year	Tournament	Surface	Partner	Opponents	Score
Loss	2023	French Open	Clay	Sander Gillé	Ivan Dodig Austin Krajicek	3–6, 1–6

Mixed doubles: 2 (2 runner-ups)

Result	Year	Tournament	Surface	Partner	Opponents	Score
Loss	2022	French Open	Clay	Ulrikke Eikeri	Ena Shibahara Wesley Koolhof	6–7(5–7), 2–6
Loss	2023	Wimbledon	Grass	Xu Yifan	Lyudmyla Kichenok Mate Pavić	4–6, 7–6(11–9), 3–6

Doubles: 12 (7 titles, 5 runner-ups)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Win	1–0	Jul 2019	Swedish Open, Sweden	250 Series	Clay	Sander Gillé	Federico Delbonis Horacio Zeballos	6–7(5–7), 7–5, [10–5]
Win	2–0	Jul 2019	Swiss Open, Switzerland	250 Series	Clay	Sander Gillé	Philipp Oswald Filip Polášek	6–4, 6–3
Loss	2–1	Aug 2019	Austrian Open, Austria	250 Series	Clay	Sander Gillé	Philipp Oswald Filip Polášek	4–6, 4–6
Win	3–1	Sep 2019	Zhuhai Championships, China	250 Series	Hard	Sander Gillé	Marcelo Demoliner Matwé Middelkoop	7–6(7–2), 7–6(7–4)
Win	4–1	Nov 2020	Astana Open, Kazakhstan	250 Series	Hard (i)	Sander Gillé	Max Purcell Luke Saville	7–5, 6–3
Win	5–1	Feb 2021	Singapore Open, Singapore	250 Series	Hard (i)	Sander Gillé	Matthew Ebden John-Patrick Smith	6–2, 6–3
Loss	5–2	May 2021	Bavarian Championships, Germany	250 Series	Clay	Sander Gillé	Wesley Koolhof Kevin Krawietz	6–4, 4–6, [5–10]
Win	6–2	Jan 2023	Maharashtra Open, India	250 Series	Hard	Sander Gillé	Sriram Balaji Jeevan Nedunchezhiyan	6–4, 6–4
Win	7–2	Apr 2023	Estoril Open, Portugal	250 Series	Clay	Sander Gillé	Nikola Ćaćić Miomir Kecmanović	6–3, 6–4
Loss	7–3	Jun 2023	French Open, France	Grand Slam	Clay	Sander Gillé	Ivan Dodig Austin Krajicek	3–6, 1–6
Loss	7–4	Jul 2023	Hamburg European Open, Germany	500 Series	Clay	Sander Gillé	Kevin Krawietz Tim Pütz	6–7(4–7), 3–6
Loss	7–5	Jan 2024	Hong Kong Open, Hong Kong	250 Series	Hard	Sander Gillé	Marcelo Arévalo Mate Pavić	6–7(3–7), 4–6

Singles: 3 (2–1)

Result	W–L	Date	Tournament	Tier	Surface	Opponent	Score
Win	1–0	Aug 2015	Belgium F8, Middelkerke	Futures	Hard	Julien Cagnina	4–6, 6–3, 7–6(7–2)
Loss	1–1	Sep 2015	Belgium F14, Middelkerke	Futures	Clay	Jeremy Jahn	3–6, 4–6
Win	2–1	Aug 2016	Belgium F11, Huy	Futures	Clay	Romain Barbosa	6–4, 6–4

Doubles: 51 (37–14)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Win	1–0	Jul 2013	Belgium F6, Heist	Futures	Clay	Cedric De Zutter	Bobbie De Goeijen Scott Griekspoor	7–5, 6–2
Win	2–0	Aug 2013	Belgium F8, Eupen	Futures	Clay	Sander Gillé	Gustavo Gómez Buyatti Antoine Hoang	6–3, 6–3
Win	3–0	Aug 2014	Belgium F11, Koksijde	Futures	Clay	Sander Gillé	Jake Eames David Pérez Sanz	3–6, 6–3, [12–10]
Win	4–0	Jun 2015	Belgium F2, Damme	Futures	Clay	Sander Gillé	Antoine Hoang Ugo Nastasi	6–2, 6–3
Loss	4–1	Jun 2015	Belgium F3, Havré	Futures	Clay	Sander Gillé	Deiton Baughman Fabrício Neis	6–2, 4–6, [2–10]
Win	5–1	Jul 2015	Belgium F7, Duinbergen	Futures	Clay	Sander Gillé	Julien Cagnina Jonas Merckx	6–7(5–7), 6–4, [10–6]
Loss	5–2	Aug 2015	Belgium F8, Middelkerke	Futures	Hard	Sander Gillé	Sander Arends Ariel Behar	7–6(7–1), 4–6, [7–10]
Loss	5–3	Aug 2015	Belgium F9, Eupen	Futures	Clay	Sander Gillé	Billy Harris Evan Hoyt	6–7(5–7), 3–6
Win	6–3	Aug 2015	Belgium F10, Koksijde	Futures	Clay	Sander Gillé	Evan Hoyt Toby Martin	6–2, 6–1
Win	7–3	Aug 2015	Belgium F11, Jupille-sur-Meuse	Futures	Clay	Sander Gillé	Evan Hoyt Toby Martin	6–1, 6–4
Win	8–3	Aug 2015	Belgium F12, Ostend	Futures	Clay	Antoine Hoang	Kevin Benning Jonas Merckx	6–2, 7–5
Win	9–3	Sep 2015	Belgium F14, Middelkerke	Futures	Clay	Gonçalo Oliveira	Timon Reichelt George von Massow	6–3, 3–6, [10–4]
Win	10–3	Oct 2015	Norway F2, Oslo	Futures	Hard (i)	Sander Gillé	Ivan Sabanov Matej Sabanov	6–7(4–7), 7–6(7–5), [10–8]
Win	11–3	Nov 2015	Norway F3, Oslo	Futures	Hard (i)	Sander Gillé	Ivan Sabanov Matej Sabanov	7–6(7–3), 6–1
Win	12–3	Jan 2016	France F2, Bressuire	Futures	Hard (i)	Sander Gillé	Benjamin Bonzi Grégoire Jacq	7–6(7–1), 7–5
Win	13–3	Jan 2016	France F3, Veigy-Foncenex	Futures	Carpet (i)	Sander Gillé	Scott Clayton Richard Gabb	6–7(4–7), 7–6(8–6), [10–7]
Loss	13–4	Mar 2016	Egypt F7, Sharm El Sheikh	Futures	Hard	Sander Gillé	Dominik Kellovský Jaroslav Pospíšil	6–3, 3–6, [11–13]
Win	14–4	Mar 2016	Egypt F8, Sharm El Sheikh	Futures	Hard	Sander Gillé	Tom Schönenberg Matthias Wunner	6–3, 7–6(7–2)
Win	15–4	Apr 2016	Uzbekistan F2, Bukhara	Futures	Hard	Sander Gillé	Evgeny Elistratov Vitaly Kozyukov	6–4, 6–3
Win	16–4	May 2016	Ukraine F1, Cherkasy	Futures	Clay	Sander Gillé	Antoine Bellier Vladyslav Manafov	6–3, 4–6, [11–9]
Win	17–4	Jun 2016	Belgium F2, Havré	Futures	Clay	Sander Gillé	Adam Taylor Jason Taylor	6–2, 6–4
Win	18–4	Jul 2016	Belgium F3, Nieuwpoort	Futures	Clay	Sander Gillé	Stijn Meulemans Laurens Verboven	6–2, 6–3
Win	19–4	Jul 2016	Belgium F6, Knokke	Futures	Clay	Sander Gillé	Hunter Johnson Yates Johnson	6–4, 6–4
Win	20–4	Jul 2016	Belgium F7, Duinbergen	Futures	Clay	Sander Gillé	Michael Geerts Jeroen Vanneste	6–7(4–7), 6–3, [10–4]
Win	21–4	Aug 2016	Trnava, Slovakia	Challenger	Clay	Sander Gillé	Tomasz Bednarek Roman Jebavý	6–2, 7–5
Loss	21–5	Aug 2016	Meerbusch, Germany	Challenger	Clay	Sander Gillé	Mikhail Elgin Andrei Vasilevski	6–7(6–8), 4–6
Loss	21–6	Aug 2016	Belgium F11, Huy	Futures	Clay	Sander Gillé	Jarryd Bant Tom Farquharson	3–6, 2–6
Loss	21–7	Jan 2017	Germany F2, Kaarst	Futures	Carpet (i)	David Pel	Jannis Kahlke Oscar Otte	3–6, 7–5, [8–10]
Win	22–7	Jan 2017	France F3, Veigy-Foncenex	Futures	Carpet (i)	Julien Dubail	Antal van der Duim Tim van Terheijden	4–6, 6–4, [10–4]
Loss	22–8	Mar 2017	Turkey F10, Antalya	Futures	Clay	Sander Gillé	Tuna Altuna Cem İlkel	6–0, 2–6, [8–10]
Win	23–8	May 2017	Italy F12, Naples	Futures	Clay	Sander Gillé	Antal van der Duim Boy Westerhof	6–4, 6–2
Win	24–8	May 2017	Romania F1, Bucharest	Futures	Clay	Sander Gillé	Andrei Ștefan Apostol Nicolae Frunză	7–6(7–5), 6–2
Win	25–8	Jun 2017	Lyon, France	Challenger	Clay	Sander Gillé	Gero Kretschmer Alexander Satschko	6–7(2–7), 7–6(7–2), [14–12]
Win	26–8	Jun 2017	Blois, France	Challenger	Clay	Sander Gillé	Máximo González Fabrício Neis	3–6, 6–3, [10–7]
Win	27–8	Jul 2017	Scheveningen, Netherlands	Challenger	Clay	Sander Gillé	Jozef Kovalík Stefanos Tsitsipas	6–2, 4–6, [12–10]
Win	28–8	Jul 2017	Tampere, Finland	Challenger	Clay	Sander Gillé	Lucas Gómez Juan Ignacio Londero	6–2, 6–7(5–7), [10–3]
Loss	28–9	Sep 2017	Sibiu, Romania	Challenger	Clay	Sander Gillé	Marco Cecchinato Matteo Donati	3–6, 1–6
Loss	28–10	Sep 2017	Rome, Italy	Challenger	Clay	Sander Gillé	Martin Kližan Jozef Kovalík	3–6, 6–7(5–7)
Win	29–10	Jan 2018	Rennes, France	Challenger	Hard (i)	Sander Gillé	Sander Arends Antonio Šančić	6–3, 6–7(1–7), [10–7]
Loss	29–11	Feb 2018	Quimper, France	Challenger	Hard (i)	Sander Gillé	Ken Skupski Neal Skupski	3–6, 6–3, [7–10]
Loss	29–12	May 2018	Rome, Italy	Challenger	Clay	Sander Gillé	Kevin Krawietz Andreas Mies	3–6, 6–2, [4–10]
Win	30–12	Jul 2018	Prague, Czech Republic	Challenger	Clay	Sander Gillé	Fernando Romboli David Vega Hernández	6–4, 6–2
Win	31–12	Aug 2018	Liberec, Czech Republic	Challenger	Clay	Sander Gillé	Filip Polášek Patrik Rikl	6–3, 6–4
Win	32–12	Aug 2018	Pullach, Germany	Challenger	Clay	Sander Gillé	Daniele Bracciali Simone Bolelli	6–2, 6–2
Win	33–12	Oct 2018	Ortisei, Italy	Challenger	Hard (i)	Sander Gillé	Purav Raja Antonio Šančić	3–6, 6–3, [10–3]
Win	34–12	Oct 2018	Brest, France	Challenger	Hard (i)	Sander Gillé	Leander Paes Miguel Ángel Reyes-Varela	3–6, 6–4, [10–2]
Win	35–12	Nov 2018	Mouilleron-le-Captif, France	Challenger	Hard (i)	Sander Gillé	Romain Arneodo Quentin Halys	6–3, 4–6, [10–2]
Loss	35–13	Jan 2019	Punta del Este, Uruguay	Challenger	Clay	Sander Gillé	Guido Andreozzi Guillermo Durán	2–6, 7–6(8–6), [8–10]
Loss	35–14	Mar 2019	Marbella, Spain	Challenger	Clay	Sander Gillé	Kevin Krawietz Andreas Mies	6–7(6–8), 6–2, [6–10]
Win	36–14	Jun 2019	Bratislava, Slovakia	Challenger	Clay	Sander Gillé	Lukáš Klein Alex Molčan	6–2, 7–5
Win	37–14	Sep 2022	Cassis, France	Challenger	Hard	Michael Geerts	Romain Arneodo Albano Olivetti	6–4, 7–6(8–6)

Doubles

Current through the 2023 Wimbledon Championships.

Mixed doubles

Current through the 2023 US Open.