2010

Quentin played in his first ITF Junior Circuit tournament in 2010 at the G4 Tournoi International de Clermont-Ferrand, as a wildcard. He lost in the first round.^[3] He reached his first final later that year, at the G5 International Junior Saint-Cyprien, in doubles. In an all-French final, Halys and Armel Rancezot lost in the super tiebreak against Julien Delaplane and Alexandre Favrot.^[4]

2011

Starting 2011, Halys entered a 17–match win streak, winning consecutively the 1st and 2nd Qatar ITF Junior Open, breaking through the qualifiers of both tournaments to win his first two singles titles. He also finished runner-up in the 1st tournament doubles.^[5][6] He streak was sniped by Belgian Clement Geens, at AEGON Junior International Nottingham, a 2-week G4 tournament. Quentin would reach the final in both singles and doubles of the 2nd week, but he won the doubles only.^[7] He would win another doubles titles in July of that year, at the Leeuwenbergh ITF G4 Junior Championships.^[8] Halys finished 2011 by playing for France at the Junior Davis Cup, where his country finished 3rd that year.^[9]

2012

Starting 2012, Quentin played in all Junior Grand Slams but Wimbledon, where he didn't pass the third round of any of them, in singles. He reached the semifinal at Australian Open doubles. Halys only final that year was at the GA Copa Gerdau, partnering Pedro Cachin, where they lost in straight sets to the partnership of Luke Bambridge and Joshua Ward-Hibbert.^[10] He played a second year for his country at the Junior Davis Cup, this time finishing in the fourth place.^[11]

2013

In 2013, Halys reached four finals in doubles, including the US Open final, where he lost to Kamil Majchrzak and Martin Redlicki, in partnership with Frederico Ferreira Silva. All other finals were at G1 tournaments, winning only at the 35° Torneo International Citta Di Santa Croce, partnering Benjamin Bonzi.^[12] In singles, he lost in the finals of the B1 European Junior Championships to Karen Khachanov.^[13]

Halys saw much success ahead of 2014, reaching 7 finals with four titles in doubles and one in singles.

2014

Partnering Johan Sébastien Tatlot, the pair reached the final of the Australian Open, where they lost in straight sets. The partnership would win the GA Porto Alegre Junior Championships (the successor of the Copa Gerdau) in March and the B1 European Junior Championships in July.^[14]

Partnering Benjamin Bonzi, the French pair won the French Open, winning in straight sets. Quentin also won the G1 Canadian Open Junior Championships in partnership with Akira Santillan, winning only two matches to win the title, as the pair received two walkovers in the semifinals and the final.^[15] Quentin reached also the US Open in singles, losing to Omar Jasika in three sets. Earlier in July, he defeated countryman Corentin Denolly to win the B1 European Junior Championships, his last singles title in junior.^[16]

2015–2017: Grand Slam debut & first two wins, first Challenger title

Halys made his Grand Slam debut at the 2015 French Open as a wildcard.

He also entered as a wildcard in the 2016 Australian Open main draw where he defeated Ivan Dodig. He lost to the top seed and eventual champion Novak Djokovic in the second round.

Again as a wildcard, he recorded his second Major win and first win on clay at the 2016 French Open over Chung Hyeon in the first round.

2021–2022: US Open debut, two more Challenger titles, Masters & top 70 debut

He reached the main draw for the third time at the 2021 Australian Open as a qualifier.

At the 2021 US Open Halys also qualified for the first time at this Major in 5 attempts.^[17] He lost in the first round to Dominik Koepfer in five sets.

January through March 2022, he won two Challenger titles at the 2022 Teréga Open Pau–Pyrénées and 2022 Play In Challenger in Lille, France and reached two more finals.

He reached the top 100 on 9 May 2022 after a quarterfinal showing at the 2022 Open du Pays d'Aix Challenger. At the 2022 French Open as a direct entry, he lost to 23rd seed John Isner in four tight sets.

On his debut at the 2022 Wimbledon Championships he won his first match at this Major defeating his compatriot Benoît Paire. He reached the top 75 at world No. 74 on 25 July 2022.

He made his Masters 1000 debut after qualifying for the 2022 Rolex Paris Masters.

He finished the year ranked world No. 64 in singles.

2023: First Masters wins & fourth round & ATP semifinal, Major third round

Halys reached the quarterfinals of an ATP tournament for the first time in his career in Auckland, after beating Alex Molčan and Ben Shelton. He lost to Jenson Brooksby in the quarterfinals.

On his debut at the 2023 Miami Open he reached the third round of a Masters 1000 for the first time having never won a match in his career at this level defeating Pedro Martinez and 15th seed Alex de Minaur in a three hours and 20 minutes match with three tiebreaks.^[18] Next he defeated Mackenzie McDonald to reach the fourth round for the first time at the Masters level.^[19] He lost to Daniil Medvedev in 70 minutes in straight sets.^[20]

In 2023 Estoril Open he reached his first ATP semifinal having won one ATP match on clay in his career (at the 2016 Rolland Garros), defeating Nuno Borges, fourth seed Roberto Bautista Agut and Dominic Thiem.^[21] He lost to top seed and eventual champion Casper Ruud in three sets.^[22]

Halys reached the third round at the 2023 Wimbledon Championships with wins over Dan Evans and Aleksandar Vukic for the first time at a Major.^[23]

Singles

Current after the 2023 Paris Masters

Doubles

Singles: 26 (12–14)

Result	W–L	Date	Tournament	Tier	Surface	Opponent	Score
Win	1–0	Oct 2014	Greece F9, Heraklion	Futures	Hard	Ricardo Rodríguez	6–3, 6–2
Loss	1–1	Feb 2015	Italy F1, Sondrio	Futures	Hard (i)	Laurynas Grigelis	7–6(9–7), 3–6, 5–7
Loss	1–2	Mar 2015	Italy F2, Trento	Futures	Carpet (i)	Philip Bester	6–3, 5–7, 3–6
Win	2–2	Mar 2015	France F6, Poitiers	Futures	Hard (i)	David Guez	7–5, 6–1
Win	3–2	Mar 2015	Great Britain F5, Shrewsbury	Futures	Hard (i)	Daniel Cox	6–4, 3–6, 6–3
Win	4–2	Aug 2015	Italy F24, Piombino	Futures	Hard	Edoardo Eremin	6–3, 6–4
Win	5–2	Sep 2015	Great Britain F8, Roehampton	Futures	Hard	Daniel Evans	6–1, 6–7(5–7), 7–5
Win	6–2	Apr 2016	Tallahassee, USA	Challenger	Clay	Frances Tiafoe	6–7(6–8), 6–4, 6–2
Loss	6–3	Oct 2016	Fairfield, USA	Challenger	Hard	Santiago Giraldo	6–4, 4–6, 2–6
Loss	6–4	Feb 2017	Bergamo, Italy	Challenger	Hard (i)	Jerzy Janowicz	4–6, 4–6
Loss	6–5	Apr 2017	Anning, China, P.R.	Challenger	Clay	Janko Tipsarević	7–6(7–5), 3–6, 4–6
Win	7–5	Feb 2018	Quimper, France	Challenger	Hard (i)	Alexey Vatutin	6–3, 7–6(7–1)
Win	8–5	Apr 2018	Nanchang, China, P.R.	Challenger	Clay (i)	Calvin Hemery	6–3, 6–2
Loss	8–6	Sep 2018	Istanbul, Turkey	Challenger	Hard	Corentin Moutet	3–6, 4–6
Loss	8–7	May 2019	Aix-en-Provence, France	Challenger	Clay	Pablo Cuevas	5–7, 6–3, 2–6
Loss	8–8	Oct 2019	M25+H Nevers, France	World Tennis Tour	Hard	Arthur Reymond	6–3, 6–7(3–7), 4–6
Loss	8–9	Jun 2021	Forlì, Italy	Challenger	Clay	Mats Moraing	6–3, 1–6, 5–7
Loss	8–10	Jul 2021	Porto, Portugal	Challenger	Hard	Altuğ Çelikbilek	2-6, 1-6
Loss	8–11	Jan 2022	Forlì, Italy	Challenger	Hard (i)	Pavel Kotov	5-7, 7-6(7-5), 3-6
Win	9–11	Feb 2022	Pau, France	Challenger	Hard (i)	Vasek Pospisil	4–6, 6–4, 6–3
Loss	9–12	Feb 2022	Turin, Italy	Challenger	Hard (i)	Mats Moraing	6-7(11-13), 3-6
Win	10–12	Mar 2022	Lille, France	Challenger	Hard (i)	Ričardas Berankis	4–6, 7–6(7–4), 6–4
Loss	10–13	May 2022	Bordeaux, France	Challenger	Clay	Alexei Popyrin	6-2, 6-7(5-7), 6-7(4-7)
Loss	10–14	Oct 2022	Orléans, France	Challenger	Hard (i)	Grégoire Barrère	6–4, 3–6, 4–6
Win	11–14	Oct 2022	Ismaning, Germany	Challenger	Carpet (i)	Max Hans Rehberg	7–6(8–6), 6–3
Win	12–14	Jun 2023	Blois, France	Challenger	Clay	Kyrian Jacquet	4-6, 6-2, 2-0 ret.

Doubles: 16 (10–6)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Win	1–0	Feb 2014	Great Britain F5, Nottingham	Futures	Hard (i)	Rémi Boutillier	Liam Broady James Cluskey	6–2, 0–6, [10–8]
Win	2–0	Jul 2014	France F14, Bourg-en-Bresse	Futures	Clay	Maxime Hamou	Maxime Forcin Ugo Nastasi	2–6, 6–2, [10–8]
Win	3–0	Oct 2014	Greece F9, Heraklion	Futures	Hard	Benjamin Bonzi	Mauricio Astorga Alberto Rojas-Maldonado	6–2, 6–4
Loss	3–1	Nov 2014	Kuwait F1, Meshref	Futures	Hard	Calvin Hemery	Juan Lizariturry Mark Vervoort	4–6, 6–7(4–7)
Loss	3–2	Jan 2015	France F1, Bagnoles-de-l'Orne	Futures	Clay (i)	Alexandre Sidorenko	Dorian Descloix Gleb Sakharov	4–6, 2–6
Loss	3–3	Oct 2016	Tiburon, USA	Challenger	Hard	Dennis Novikov	Matt Reid John-Patrick Smith	1–6, 2–6
Win	4–3	Jan 2017	Nouméa, New Caledonia	Challenger	Hard	Tristan Lamasine	Adrián Menéndez Maceiras Stefano Napolitano	7–6(11–9), 6–1
Win	5–3	Jul 2017	Recanati, Italy	Challenger	Hard	Jonathan Eysseric	Julian Ocleppo Andrea Vavassori	6–7(3–7), 6–4, [12–10]
Loss	5–4	Nov 2018	Mouilleron-le-Captif, France	Challenger	Hard (i)	Romain Arneodo	Sander Gillé Joran Vliegen	3–6, 6–4, [2–10]
Win	6–4	May 2019	Bordeaux, France	Challenger	Clay	Grégoire Barrère	Romain Arneodo Hugo Nys	6–4, 6–1
Loss	6–5	Oct 2019	M25+H Nevers, France	World Tennis Tour	Hard	Matteo Martineau	Dan Added Albano Olivetti	4–6, 5–7
Win	7–5	Oct 2019	Ismaning, Germany	Challenger	Carpet (i)	Tristan Lamasine	Maxime Cressy James Cerretani	6–3, 7–5
Win	8–5	Mar 2021	Biella, Italy	Challenger	Hard (i)	Tristan Lamasine	Denys Molchanov Sergiy Stakhovsky	6-1, 2-0 ret.
Win	9-5	Oct 2021	Mouilleron-le-Captif, France	Challenger	Hard (i)	Jonathan Eysseric	David Pel Aisam-ul-Haq Qureshi	4–6, 7–6(7–5), [10–8]
Win	10-5	Feb 2022	Cherbourg, France	Challenger	Hard (i)	Jonathan Eysseric	Hendrik Jebens Niklas Schell	7–6(8–6), 6–2
Loss	10–6	Mar 2022	Lille, France	Challenger	Hard (i)	Jonathan Eysseric	Viktor Durasovic Patrik Niklas-Salminen	5-7, 6-7(1-7)

Singles: 1 (1 runner-up)

Result	Year	Tournament	Surface	Opponent	Score
Loss	2014	US Open	Hard	Omar Jasika	6–2, 5–7, 1–6

Doubles: 3 (1 title, 2 runner-ups)

Result	Year	Tournament	Surface	Partner	Opponents	Score
Loss	2013	US Open	Hard	Frederico Ferreira Silva	Kamil Majchrzak Martin Redlicki	3–6, 4–6
Loss	2014	Australian Open	Hard	Johan Tatlot	Lucas Miedler Bradley Mousley	4–6, 3–6
Win	2014	French Open	Clay	Benjamin Bonzi	Renta Tokuda Jumpei Yamasaki	6–4, 3–6. [10–3]

Singles: 6 (4 titles, 2 runner-ups)

Result	W–L	Date	Tournament	Category	Surface	Opponent	Score
Win	1–0	Feb 2011	1st Qatar ITF Junior Open, Qatar	Grade 5	Hard	Johan Skattum	6–3, 6–0
Win	2–0	Apr 2011	2nd Qatar ITF Junior Open, Qatar	Grade 5	Hard	Maxime Hamou	6–7(6–8), 6–4, 6–2
Win	3–0	Apr 2011	AEGON Junior International Nottingham (2nd week), UK	Grade 4	Hard	Max de Vroome	6–1, 5–7, 6–1
Loss	3–1	Jul 2013	European Junior Championships, Switzerland	Grade B1	Clay	Karen Khachanov	6–4, 3–6, 4–6
Win	4–1	Jul 2014	European Junior Championships, Switzerland	Grade B1	Clay	Corentin Denolly	6–4, 7–5
Loss	4–2	Sep 2014	US Open, United States	Grade A	Hard	Omar Jasika	6–2, 5–7, 1–6

Doubles: 14 (7 titles, 7 runner-ups)

Outcome	Date	Category	Tournament	Surface	Partner	Opponents	Score
Runner-up	7 November 2010	Grade 5	International Junior Saint-Cyprien, France	Hard (i)	Armel Rancezot	Julien Delaplane Alexandre Favrot	6–7(2–7), 6–4, [5–10]
Runner-up	4 February 2011	Grade 5	1st Qatar ITF Junior Open, Qatar	Hard	Florian Lakat	Chun Hun Wong Pak Long Yeung	1–6, 4–6
Winner	18 April 2011	Grade 4	AEGON Junior International Nottingham (2nd week), United Kingdom	Hard	Maxime Hamou	Toby Martin Toby Mitchell	6–3, 7–6(7–5)
Winner	10 July 2011	Grade 4	Leeuwenbergh ITF Junior Championships, Netherlands	Clay	Maxime Hamou	Harry Bourchier Henrique Sousa	3–6, 6–2, 10–5
Runner-up	25 March 2012	Grade A	29th Copa Gerdau, Brazil	Clay	Pedro Cachin	Luke Bambridge Joshua Ward-Hibbert	5–7, 5–7
Runner-up	17 March 2013	Grade 1	43rd Banana Bowl, Brazil	Clay	Pedro Cachin	Stefan Kozlov Spencer Papa	6–4, 3–6, [7–10]
Runner-up	28 April 2013	Grade 1	18ème Open International Junior, France	Clay	Alexander Muller	Johannes Härteis Hannes Wagner	2–6, 4–6
Winner	18 May 2013	Grade 1	35° Torneo International Citta Di Santa Croce, Italy	Clay	Benjamin Bonzi	Rafael Matos Marcelo Zormann	6–2, 6–2
Runner-up	9 September 2013	Grade A	US Open, United States	Hard	Frederico Ferreira Silva	Kamil Majchrzak Martin Redlicki	3–6, 4–6
Runner-up	25 January 2014	Grade A	Australian Open, Australia	Hard	Johan Sébastien Tatlot	Lucas Miedler Bradley Mousley	4–6, 3–6
Winner	30 March 2014	Grade A	Porto Alegre Junior Championships, Brazil	Clay	Johan Sébastien Tatlot	Renta Tokuda Jumpei Yamasaki	6–4, 3–6, [10–3]
Winner	7 June 2014	Grade A	French Open, France	Clay	Benjamin Bonzi	Lucas Miedler Akira Santillan	6–4, 6–3
Winner	27 July 2014	Grade B1	European Junior Championships, Switzerland	Clay	Johan Sébastien Tatlot	Tallon Griekspoor Tim van Rijthoven	6–2, 6–4
Winner	30 August 2014	Grade 1	Canadian Open Junior Championships, Canada	Hard	Akira Santillan	Naoki Nakagawa Tim van Rijthoven	Walkover