2019: Grand Slam debut and first two wins, Top 100

During the 2019 Australian Open, Majchrzak advanced through the qualifying to reach the 1st round. He won the first two sets against top-10 player Kei Nishikori, but then was forced to retire due to an injury.^[4]

In March 2019 Majchrzak celebrated his maiden Challenger triumph at the 2019 Open Harmonie mutuelle in St. Brieuc, France. Two months later he advanced to the 2019 Prosperita Open final with wins over Riccardio Bonadio, Zsombor Piros, No. 5 seeded Dennis Novak, top seed Lloyd Harris and Jannik Sinner to lift his second ATP Challenger trophy.^[5]

Majchrzak made the semifinals of the 2019 Ilkley Trophy Challenger and then qualified for Wimbledon without dropping a set. In the first round at Wimbledon he lost to Fernando Verdasco. At the 2019 Hall of Fame Open in Rhode Island he defeated Alastair Gray before losing a three set match to No. 1 seed John Isner in the second round.^[6] As a result, he reached the top 100 on 29 July 2019.

At the 2019 US Open, Majchrzak lost in the final round of qualifying. With the sudden withdrawal of Milos Raonic, he came in as a lucky loser, and defeated Nicolás Jarry and Pablo Cuevas – both in five-set thrillers to reach the third round at a Grand Slam for the first time in his career. He fell to Grigor Dimitrov in straight sets in the third round. He reached a new career-high of No. 83 on 23 September.

2020: Inaugural ATP Cup, Injury and return

At the start of the year, Majchrzak participated in the inaugural 2020 ATP Cup before suffering from a broken pelvic bone.^[7] Subsequently, Majchrzak had to withdraw from the 2020 Australian Open and Maharashtra Open due to a groin injury.^[8] He would not compete again for more than seven months.

In August he returned to tennis and participated at the US Open where he lost to Ernesto Escobedo in the first round. He then transitioned to clay courts and on 13 September 2020 won his third Challenger title at the 2020 Czech Open. In the final, he defeated top seed and defending champion Pablo Andújar.^[9]

Majchrzak entered at the 2020 French Open with a protected ranking. In the first round he lost to 15th seeded Karen Khachanov.

2021: Masters & Olympics debut, First ATP quarterfinal

Majchrzak started his season at the 2021 Great Ocean Road Open in Melbourne, Australia, which was organized as a lead-up tournament to the 2021 Australian Open. He entered under a protected ranking and in the first round defeated Laslo Đere in straight sets.

He used his protected ranking as well to enter the main draw of the 2021 French Open and also reached the second round with a win over Arthur Cazaux.

Majchrzak qualified to represent Poland at the 2020 Summer Olympics where he was defeated by Miomir Kecmanović in the first round.

Majchrzak qualified at the 2021 Sofia Open as a lucky loser after the withdrawal of fourth seed Alexander Bublik. He reached the quarterfinals of an ATP tournament for the first time in his career by defeating wildcard Dimitar Kuzmanov.^[10]

2022–2023: ATP Cup semifinalist, top 75, doping suspension

At the 2022 ATP Cup, Majchrzak won all his three matches and helped Poland reach the semifinals for the first time,^[7] before testing positive for COVID-19 and having to withdraw late from the tournament. As a result, he was unable to participate at the 2022 Australian Open qualifications where he was seeded fourth and thus possibly missing the first Grand Slam of the year.^[11] He nevertheless entered the main draw after replacing Jenson Brooksby who withdrew due to COVID-19. He reached the second round for the first time at this Major with a win over Andreas Seppi. Majchrzak lost to Alex de Minaur in the second round.^[12]

At the 2022 Tata Open Maharashtra he reached the semifinals of an ATP tournament for the first time in his career defeating second seed Lorenzo Musetti.^[13] As a result, he reached the top 75 in the rankings on 28 February 2022.

In May at the 2022 Geneva Open he clinched the biggest win of his career defeating 8th seed and World No. 41 Alexander Bublik in the first round in straight sets.^[14][15] He reached the quarterfinals only for the third time in his career defeating qualifier Marco Cecchinato.^[16]

In September at the 2022 Sofia Open he reached his third tour-level quarterfinal of the season, for a second year in a row, defeating Ričardas Berankis and eight seed Oscar Otte.^[17] He lost to eventual champion Marc-Andrea Huesler.^[18] At the 2022 Busan Open in South Korea, he won his fourth Challenger title defeating Radu Albot. As a result, he moved 20 positions up back into the top 100 at No. 82 on 24 October 2022.

On 9 December 2022, the International Tennis Integrity Agency announced that Majchrzak has been provisionally suspended after testing positive for banned substances at the Sofia Open, the Japan Open and the Seoul Challenger.^[19][20][21] In June 2023, the agency suspended Majchrzak for 13 months, while acknowledging that Majchrzak had not "knowingly or intentionally" committed an offense.^[22]

Singles

Current through the 2022 Miami Open.

Singles: 23 (13–10)

Result	W–L	Date	Tournament	Tier	Surface	Opponent	Score
Win	1–0	Mar 2014	Spain F4, Cartagena	Futures	Clay	Roberto Carballés Baena	1–6, 7–6(7–4), 6–3
Win	2–0	Jul 2014	Slovakia F2, Michalovce	Futures	Clay	Filip Brtnický	6–2, 6–3
Loss	2–1	Sep 2014	Poland F7, Piekary Śląskie	Futures	Clay	Dušan Lojda	6–4, 3–6, 6–7(3–7)
Loss	2–2	Jan 2015	Egypt F2, Cairo	Futures	Clay	Mohamed Safwat	5–7, 3–6
Loss	2–3	Feb 2015	Egypt F3, Cairo	Futures	Clay	Laslo Đere	3–6, 5–7
Win	3–3	Apr 2015	Spain F9, Reus	Futures	Clay	Marc Giner	6–3, 6–2
Win	4–3	May 2015	Romania F4, Bacău	Futures	Clay	Dragoș Dima	6–1, 6–2
Loss	0–1	Oct 2015	Mohammedia, Morocco	Challenger	Clay	Roberto Carballés Baena	6–7(4–7), 2–6
Loss	4–4	May 2016	Hungary F2, Szeged	Futures	Clay	Germain Gigounon	4–6, 3–6
Win	5–4	May 2016	Ukraine F2, Cherkassy	Futures	Clay	Vladyslav Manafov	6–2, 6–4
Win	6–4	Jun 2016	Poland F3, Sopot	Futures	Clay	Andriej Kapaś	7–5, 6–4
Win	7–4	Jan 2017	Turkey F1, Antalya	Futures	Hard	Liam Broady	5–7, 6–3, 6–3
Loss	7–5	Jun 2017	Poland F1, Sopot	Futures	Clay	Zdeněk Kolář	3–6, 2–6
Loss	0–2	Oct 2017	Tashkent, Uzbekistan	Challenger	Hard	Guillermo García López	1–6, 6–7(1–7)
Win	8–7	Oct 2017	France F24, Rodez	Futures	Hard (i)	Antoine Hoang	7–6(7–3), 2–6, 6–1
Loss	0–3	Oct 2018	Tashkent, Uzbekistan	Challenger	Hard	Félix Auger-Aliassime	3–6, 2–6
Win	1–3	Mar 2019	Saint Brieuc, France	Challenger	Hard (i)	Maxime Janvier	6–3, 7–6(7–1)
Win	2–3	May 2019	Ostrava, Czech Republic	Challenger	Clay	Jannik Sinner	6–1, 6–0
Win	3–3	Sep 2020	Prostějov, Czech Republic	Challenger	Clay	Pablo Andújar	6–2, 7–6(7–5)
Loss	3–4	Jun 2021	Nottingham, United Kingdom	Challenger	Grass	Alex Bolt	6–4, 4–6, 3–6
Loss	3–5	Sep 2021	Szczecin, Poland	Challenger	Clay	Zdeněk Kolář	6–7(4–7), 5–7
Win	4–5	Oct 2022	Busan, South Korea	Challenger	Hard	Radu Albot	6–4, 3–6, 6–2
Win	5–2	Jan 2024	Tunisia F1, Monastir	Futures	Hard (i)	Ryuki Matsuda	6–1, 6–1

Doubles: 11 (6–5)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Loss	0–1	Aug 2013	Poland F4, Poznań	Futures	Clay	Phillip Gresk	Romain Arneodo Benjamin Balleret	2–6, 4–6
Win	1–1	Jan 2015	Egypt F2, Cairo	Futures	Clay	Maxime Janvier	Na Jung-woong Yun Jae-won	6–2, 6–2
Loss	0–1	Sep 2015	Seville, Spain	Challenger	Clay	Marco Bortolotti	Wesley Koolhof Matwé Middelkoop	6–7(5–7), 4–6
Loss	0–2	Sep 2015	Trnava, Slovakia	Challenger	Clay	Stéphane Robert	Wesley Koolhof Matwé Middelkoop	4–6, 2–6
Win	2–1	Feb 2016	Spain F2, Paguera	Futures	Clay	Tomislav Brkić	Carlos Taberner Kento Yamada	6–3, 6–4
Loss	2–2	May 2016	Ukraine F2, Cherkassy	Futures	Clay	Federico Maccari	Vladimir Ivanov Lukas Mugevičius	3–6, 3–6
Win	3–2	Jun 2016	Netherlands F2, Breda	Futures	Clay	Tomislav Brkić	Karim-Mohamed Maamoun Ilija Vučić	6–0, 6–2
Loss	0–3	Sep 2015	Poznań, Poland	Challenger	Clay	Mateusz Kowalczyk	Aleksandre Metreveli Peng Hsien-yin	4–6, 6–3, [8–10]
Win	4–2	Mar 2017	Turkey F9, Antalya	Futures	Clay	Pedro Sakamoto	Pedro Bernardi Christopher Díaz Figueroa	6–2, 6–2
Win	5–2	Jun 2017	Czech Republic F3, Jablonec nad Nisou	Futures	Clay	Jan Choinski	Petr Michnev Matej Vocel	7–6(7–4), 6–3
Win	1-3	Oct 2020	Hamburg, Germany	Challenger	Hard (i)	Marc-Andrea Hüsler	Lloyd Glasspool Alex Lawson	6–3, 1–6, [20–18]

Junior Grand Slam Finals

Doubles: 1 (1 title)

Result	Year	Tournament	Surface	Partner	Opponent	Score
Win	2013	US Open	Hard	Martin Redlicki	Quentin Halys Frederico Ferreira Silva	6–3, 6–4

Olympic medal matches

Singles

Outcome	Year	Championship	Surface	Opponents	Score
Gold	2014	Nanjing Youth Olympics	Hard	Orlando Luz	6–4, 7–5

Mixed doubles

Outcome	Year	Championship	Surface	Partner	Opponents	Score
Bronze	2014	Nanjing Youth Olympics	Hard	Fanni Stollár	Ioana Ducu Matías Zukas	6–3, 3–6, [10–5]