2015-16: Partnership with Middelkoop, First ATP & 11 Challengers titles

Koolhof won his maiden ATP tour doubles title at the 2016 Sofia Open on indoor hard courts in Bulgaria, partnering compatriot Matwe Middelkoop. The pair defeated Adil Shamasdin and Philipp Oswald in a third set tie-breaker 5–7, 7–6^(11–9), [10–6] in the championship match to capture the title.

2017-18: New partnership with Sitak, Five ATP finals

Koolhof teamed up with New Zealand player Artem Sitak mid-year in 2017. They reached the final at the 2017 BB&T Atlanta Open, losing to the Bryan brothers, and lost in the first round at the US Open before winning a Challenger event in Szczecin, Poland, and losing another ATP final, this time at the 2017 Moselle Open in Metz, France, to Julien Benneteau and Édouard Roger-Vasselin.

Starting the new 2018 year in Brisbane, Sitak and Koolhof lost in the semi-finals to Leonardo Mayer and Horacio Zeballos. They lost in the first round in Auckland to Michael Venus and Raven Klaasen, and then 7–6⁽⁵⁾, 4–6, 4–6 in the second round of the Australian Open to the eventual winners, Oliver Marach and Mate Pavić.

Sitak and Koolhof then went to Newport Beach in California where, as top seeds, they lost in the first round in straight sets to Treat Huey and Denis Kudla. They then lost in the quarterfinals at Montpellier before going all the way to the final in the New York Open, being beaten by Max Mirnyi and Philipp Oswald in a match tie-break. They followed that up with a first round loss at Delray Beach to Scott Lipsky and Divij Sharan.

Their up and down season continued in Brazil, where they reached the final in São Paulo, but were beaten in straight sets by Federico Delbonis and Máximo González. Their next stop was Irving, Texas, where they lost in the semifinals of the ATP Challenger to Alexander Peya and Philipp Petzschner. Moving to Europe, and playing in the Alicante Challenger in Spain as preparation for the European clay court season, they won their second title together when they beat Guido Andreozzi and Ariel Behar in the final in straight sets. They lost in the first round of their next tournament in Marrakech. In the Hungarian Open they beat the top seeds Nikola Mektic and Alexander Peya in the first round, but lost in the second to Marcin Matkowski and Sitak's former partner Nicholas Monroe.

Their next tournament was at Estoril where they went all the way to the final before losing to the British pair of Kyle Edmund and Cameron Norrie. They then lost in the first round of the Bordeaux Challenger tournament after Sitak had been hit in the right ear by a smash from Radu Albot, and also in the first round in Geneva, the last tournament before the French Open.

At Roland Garros, Sitak and Koolhof beat Andre Begemann and Antonio Sancic in the first round, then the ninth seeds Ivan Dodig and Rajeev Ram, before going down to fifth seeds Juan Sebastian Cabal and Robert Farah. All three matches went to a deciding set. After the tournament was finished, it was announced that the pair would split, with Koolhof joining Sitak's fellow New Zealander, and former partner, Marcus Daniell, and Sitak linking up with Indian Divij Sharan.^[4]

2019: First Major quarterfinal with Daniell, Three Masters finals

Koolhof partnering with Stefanos Tsitsipas reached his first Masters 1000 final at the 2019 Miami Open losing to the Bryan brothers and with Robin Haase made the finals of the 2019 Monte-Carlo Masters and the 2019 Canadian Open.

At the 2019 Wimbledon Championships he reached the quarterfinals partnering Marcus Daniell in doubles and the semifinals in mixed doubles with Květa Peschke.

2020: ATP Finals title & US Open final with Mektic, World No. 5

2020 was the most successful year for Koolhof in his career thus far. He won the 2020 ATP Finals in doubles partnering Nikola Mektić. He also reached the doubles semifinal of the 2020 French Open and the final at the 2020 US Open partnering again with Nikola Mektić. As a result he finished the year at world No. 5 in the top 10 rankings in doubles and No. 3 in the doubles race with his partner Nikola Mektić.

2021: Seventh title, Second mixed doubles semifinal, Olympics debut

In May, Koolhof won his seventh title at the 2021 Bavarian Championships with Kevin Krawietz. He also reached his 7th and 8th consecutive Masters 1000 quarterfinals at the 2021 Mutua Madrid Open with Łukasz Kubot and at the 2021 Italian Open with compatriot Jean-Julien Rojer.^[5]

2022: Partnership with Skupski, three Masters & mixed doubles titles, World No. 1

Partnering with Neal Skupski he won two ATP 250 titles during the Australian Summer swing, before the 2022 Australian Open. The pair reached the quarterfinals at the first Grand Slam of the year for the first time at this Major. They won their third title at the 2022 Qatar ExxonMobil Open dropping only one set en route to the final where they defeated Rohan Bopanna and Denis Shapovalov in straight sets.^[6] He reached the final of the 2022 Miami Open with Skupski where they lost to John Isner and Hubert Hurkacz.

Seeded seventh, they reached their second Masters 1000 final at the 2022 Mutua Madrid Open after defeating John Isner and Hubert Hurkacz.^[7] In the final they defeated fifth seeds Robert Farah and Juan Sebastián Cabal to win their first Masters 1000 title in their career and as a pair.^[8] As a result Koolhof returned to the top 10 in the rankings on 9 May 2022.

At the 2022 French Open he won his first Grand Slam title in mixed doubles in his career partnering Ena Shibahara.^[9] He also reached the quarterfinals with Skupski for the second time at this Major defeating unseeded pair of Americans Tommy Paul and Mackenzie McDonald. ^[10]

He reached a new career high doubles ranking of World No. 4 on 8 August at the start of the 2022 National Bank Open where he reached with Skupski the semifinals of a Masters 1000 for the third time in the season defeating Lloyd Glasspool/Harri Heliövaara.^[11] Next the pair advanced to the eight final of the season defeating Krawietz/Mies.^[12] They won their sixth title defeating Dan Evans (tennis) and John Peers (tennis).^[13] As a result he moved to world No. 3 in the doubles rankings on 15 August 2022.

Seeded 2nd at the US Open the pair reached the quarterfinals defeating Wimbledon champions Australian pair of Ebden/Purcell in three sets.^[14] Next they defeated Marcelo Demoliner and Joao Sousa to reach the semifinals. They reached the finals after defeating Marcelo Arevalo and Jean-Julien Rojer in the semifinals for a chance to become World No. 1.^[15] In the finals, they lost in straight sets to Rajeev Ram and Joe Salisbury.^[16] At the 2022 Rolex Paris Masters the pair Koolhof/Skupski reached the semifinals defeating ninth seeds Rohan Bopanna/Matwe Middelkoop climbing to World No. 1 and World No. 2 respectively, and solidifying the No. 1 position as a pair in the doubles race.^[17] They reached their 10th final and fourth at a Masters level for the season defeating seventh seeds Lloyd Glasspool /Harri Heliövaara.^[18] They won their third Masters title and seventh for the season defeating eight seeds Ivan Dodig/Austin Krajicek in the final.^[19] They also clinched the No. 1 year-end ranking as a team.^[20][21]

2023: Wimbledon Champion, Indian Wells finalist, 15th title

The world No. 1 duo Koolhof and Skupsi continued their good form reaching yet another Masters final at the 2023 BNP Paribas Open where they lost to Rohan Bopanna and Matthew Ebden.

At the 2023 French Open he reached the quarterfinals with Skupski for the third time in his career. He lost to the 10th seeded team of Horacio Zeballos and Marcel Granollers.

He won his first Grand Slam title at the 2023 Wimbledon Championships with Skupski and returned to the No. 1 ranking.

On 28 November 2023, he announced that the 2024 season would be his last on the tour.^[22]

2024: Last season on tour

Grand Slam tournament finals

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

Result	Year	Championship	Surface	Partner	Opponents	Score
Loss	2020	US Open	Hard	Nikola Mektić	Mate Pavić Bruno Soares	5–7, 3–6
Loss	2022	US Open	Hard	Neal Skupski	Rajeev Ram Joe Salisbury	6–7(4–7), 5–7
Win	2023	Wimbledon	Grass	Neal Skupski	Marcel Granollers Horacio Zeballos	6–4, 6–4

Mixed doubles: 1 (title)

Result	Year	Tournament	Surface	Partner	Opponents	Score
Win	2022	French Open	Clay	Ena Shibahara	Ulrikke Eikeri Joran Vliegen	7–6(7–5), 6–2

Year-end championships

Doubles: 1 (1 title)

Result	Year	Championship	Surface	Partner	Opponents	Score
Win	2020	ATP Finals, London	Hard (i)	Nikola Mektić	Jürgen Melzer Édouard Roger-Vasselin	2–6, 6–3, [10–5]

Masters 1000

Doubles: 8 (3 titles, 5 runner-ups)

Result	Year	Tournament	Surface	Partner	Opponents	Score
Loss	2019	Miami Open	Hard	Stefanos Tsitsipas	Bob Bryan Mike Bryan	5–7, 6–7(8–10)
Loss	2019	Monte-Carlo Masters	Clay	Robin Haase	Nikola Mektić Franko Škugor	7–6(7–3), 6–7(3–7), [9–11]
Loss	2019	Canadian Open	Hard	Robin Haase	Marcel Granollers Horacio Zeballos	5–7, 5–7
Loss	2022	Miami Open	Hard	Neal Skupski	Hubert Hurkacz John Isner	6–7(5–7), 4–6
Win	2022	Madrid Open	Clay	Neal Skupski	Juan Sebastián Cabal Robert Farah	6–7(4–7), 6–4, [10–5]
Win	2022	Canadian Open	Hard	Neal Skupski	Dan Evans John Peers	6–2, 4–6, [10–6]
Win	2022	Paris Masters	Hard (i)	Neal Skupski	Ivan Dodig Austin Krajicek	7–6(7–5), 6–4
Loss	2023	Indian Wells Masters	Hard	Neal Skupski	Rohan Bopanna Matthew Ebden	3–6, 6–2, [8–10]

Doubles: 38 (17 titles, 21 runner-ups)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Win	1–0	Feb 2016	Sofia Open, Bulgaria	250 Series	Hard (i)	Matwé Middelkoop	Philipp Oswald Adil Shamasdin	5–7, 7–6(11–9), [10–6]
Win	2–0	Jul 2016	Austrian Open, Austria	250 Series	Clay	Matwé Middelkoop	Dennis Novak Dominic Thiem	2–6, 6–3, [11–9]
Win	3–0	Jan 2017	Sydney International, Australia	250 Series	Hard	Matwé Middelkoop	Jamie Murray Bruno Soares	6–3, 7–5
Loss	3–1	Feb 2017	Rotterdam Open, Netherlands	500 Series	Hard (i)	Matwé Middelkoop	Ivan Dodig Marcel Granollers	6–7(5–7), 3–6
Loss	3–2	Jul 2017	Atlanta Open, United States	250 Series	Hard	Artem Sitak	Bob Bryan Mike Bryan	3–6, 4–6
Loss	3–3	Sep 2017	Moselle Open, France	250 Series	Hard (i)	Artem Sitak	Julien Benneteau Édouard Roger-Vasselin	5–7, 3–6
Loss	3–4	Feb 2018	New York Open, United States	250 Series	Hard (i)	Artem Sitak	Max Mirnyi Philipp Oswald	4–6, 6–4, [6–10]
Loss	3–5	Mar 2018	Brasil Open, Brazil	250 Series	Clay (i)	Artem Sitak	Federico Delbonis Máximo González	4–6, 2–6
Loss	3–6	May 2018	Estoril Open, Portugal	250 Series	Clay	Artem Sitak	Kyle Edmund Cameron Norrie	4–6, 2–6
Loss	3–7	Oct 2018	Stockholm Open, Sweden	250 Series	Hard (i)	Marcus Daniell	Luke Bambridge Jonny O'Mara	5–7, 6–7(8–10)
Win	4–7	Jan 2019	Brisbane International, Australia	250 Series	Hard	Marcus Daniell	Rajeev Ram Joe Salisbury	6–4, 7–6(8–6)
Loss	4–8	Mar 2019	Miami Open, United States	Masters 1000	Hard	Stefanos Tsitsipas	Bob Bryan Mike Bryan	5–7, 6–7(8–10)
Loss	4–9	Apr 2019	Monte-Carlo Masters, Monaco	Masters 1000	Clay	Robin Haase	Nikola Mektić Franko Škugor	7–6(7–3), 6–7(3–7), [9–11]
Loss	4–10	Apr 2019	Hungarian Open, Hungary	250 Series	Clay	Marcus Daniell	Ken Skupski Neal Skupski	3–6, 4–6
Loss	4–11	Jun 2019	Rosmalen Championships, Netherlands	250 Series	Grass	Marcus Daniell	Dominic Inglot Austin Krajicek	4–6, 6–4, [4–10]
Loss	4–12	Jul 2019	German Open, Germany	500 Series	Clay	Robin Haase	Oliver Marach Jürgen Melzer	2–6, 6–7(3–7)
Loss	4–13	Aug 2019	Canadian Open, Canada	Masters 1000	Hard	Robin Haase	Marcel Granollers Horacio Zeballos	5–7, 5–7
Win	5–13	Jan 2020	Qatar Open, Qatar	250 Series	Hard	Rohan Bopanna	Luke Bambridge Santiago González	3–6, 6–2, [10–6]
Loss	5–14	Feb 2020	Open 13, France	250 Series	Hard (i)	Nikola Mektić	Nicolas Mahut Vasek Pospisil	3–6, 4–6
Loss	5–15	Sep 2020	US Open, United States	Grand Slam	Hard	Nikola Mektić	Mate Pavić Bruno Soares	5–7, 3–6
Win	6–15	Nov 2020	ATP Finals, United Kingdom	Tour Finals	Hard (i)	Nikola Mektić	Jürgen Melzer Édouard Roger-Vasselin	2–6, 6–3, [10–5]
Win	7–15	May 2021	Bavarian Championships, Germany	250 Series	Clay	Kevin Krawietz	Sander Gillé Joran Vliegen	4–6, 6–4, [10–5]
Loss	7–16	Oct 2021	European Open, Belgium	250 Series	Hard (i)	Jean-Julien Rojer	Nicolas Mahut Fabrice Martin	0–6, 1–6
Win	8–16	Jan 2022	Melbourne Summer Set 1, Australia	250 Series	Hard	Neal Skupski	Aleksandr Nedovyesov Aisam-ul-Haq Qureshi	6–4, 6–4
Win	9–16	Jan 2022	Adelaide International 2, Australia	250 Series	Hard	Neal Skupski	Ariel Behar Gonzalo Escobar	7–6(7–5), 6–4
Win	10–16	Feb 2022	Qatar Open, Qatar (2)	250 Series	Hard	Neal Skupski	Rohan Bopanna Denis Shapovalov	7–6(7–4), 6–1
Loss	10–17	Apr 2022	Miami Open, United States	Masters 1000	Hard	Neal Skupski	Hubert Hurkacz John Isner	6–7(5–7), 4–6
Loss	10–18	Apr 2022	Barcelona Open, Spain	500 Series	Clay	Neal Skupski	Kevin Krawietz Andreas Mies	7–6(7–3), 6–7(5–7), [6–10]
Win	11–18	May 2022	Madrid Open, Spain	Masters 1000	Clay	Neal Skupski	Juan Sebastián Cabal Robert Farah	6–7(4–7), 6–4, [10–5]
Win	12–18	Jun 2022	Rosmalen Championships, Netherlands	250 Series	Grass	Neal Skupski	Matthew Ebden Max Purcell	4–6, 7–5, [10–6]
Win	13–18	Aug 2022	Canadian Open, Canada	Masters 1000	Hard	Neal Skupski	Dan Evans John Peers	6–2, 4–6, [10–6]
Loss	13–19	Sep 2022	US Open, United States	Grand Slam	Hard	Neal Skupski	Rajeev Ram Joe Salisbury	6–7(4–7), 5–7
Win	14–19	Nov 2022	Paris Masters, France	Masters 1000	Hard (i)	Neal Skupski	Ivan Dodig Austin Krajicek	7–6(7–5), 6–4
Loss	14–20	Mar 2023	Indian Wells Masters, United States	Masters 1000	Hard	Neal Skupski	Rohan Bopanna Matthew Ebden	3–6, 6–2, [8–10]
Loss	14–21	Apr 2023	Barcelona Open, Spain	500 Series	Clay	Neal Skupski	Máximo González Andrés Molteni	3–6, 7–6(10–8), [4–10]
Win	15–21	Jun 2023	Rosmalen Championships, Netherlands (2)	250 Series	Grass	Neal Skupski	Gonzalo Escobar Aleksandr Nedovyesov	7–6(7–1), 6–2
Win	16–21	Jul 2023	Wimbledon Championships, United Kingdom	Grand Slam	Grass	Neal Skupski	Marcel Granollers Horacio Zeballos	6–4, 6–4
Win	17–21	Jan 2024	Auckland Open, New Zealand	250 Series	Hard	Nikola Mektić	Marcel Granollers Horacio Zeballos	6–3, 6–7(5–7), [10–7]

Doubles: 14

Date	Tournament	Surface	Partner	Opponents	Score
17 November 2013	Guayaquil, Ecuador	Clay	Stephan Fransen	Roman Borvanov Alexander Satschko	1–6, 6–2, [10–5]
27 July 2014	Oberstaufen, Germany	Clay	Alessandro Motti	Radu Albot Mateusz Kowalczyk	7–6(9–7), 6–3
6 February 2015	Glasgow, United Kingdom	Hard (i)	Matwé Middelkoop	Sergei Bubka Aleksandr Nedovyesov	6–1, 6–4
2 May 2015	Turin, Italy	Clay	Matwé Middelkoop	Dino Marcan Antonio Šančić	4–6, 6–3, [10–5]
4. July 2015	Marburg, Germany	Clay	Matwé Middelkoop	Tobias Kamke Simon Stadler	6–1, 7–5
15 August 2015	Prague, Czech Republic	Clay	Matwé Middelkoop	Sergey Betov Mikhail Elgin	6–4, 3–6, [10–7]
11 September 2015	Seville, Spain	Clay	Matwé Middelkoop	Marco Bortolotti Kamil Majchrzak	7–6(7–5), 6–4
26 September 2015	Trnava, Slovakia	Clay	Matwé Middelkoop	Kamil Majchrzak Stéphane Robert	6–4, 6–2
25 October 2015	Brest, France	Hard (i)	Matwé Middelkoop	Ken Skupski Neal Skupski	3–6, 6–4, [10–6]
16 January 2016	Bangkok, Thailand	Hard	Matwé Middelkoop	Gero Kretschmer Alexander Satschko	6–3, 7–6(7–1)
19 June 2016	Ilkley, United Kingdom	Grass	Matwé Middelkoop	Marcelo Demoliner Aisam-ul-Haq Qureshi	7–6(7–5), 0–6, [10–8]
31 July 2016	Scheveningen, Netherlands	Clay	Matwé Middelkoop	Tallon Griekspoor Tim van Rijthoven	6–1, 3–6, [13–11]
26 November 2016	Andria, Italy	Carpet (i)	Matwé Middelkoop	Roman Jebavý Zdeněk Kolář	6–3, 6–3
13 May 2017	Aix-en-Provence, France	Clay	Matwé Middelkoop	Andre Begemann Jérémy Chardy	2–6, 6–4, [16–14]

Men's doubles

Current through the 2023 ATP Finals.

Mixed doubles