[3] Partnered with Martin Redlicki, Majchrzak won the 2013 US Open boys' doubles title by defeating Quentin Halys and Frederico Ferreira Silva in the final.

At the 2019 Hall of Fame Open in Rhode Island he defeated Alastair Gray before losing a three set match to No.

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.

At the start of the year, Majchrzak participated in the inaugural 2020 ATP Cup before suffering from a broken pelvic bone.

He began to turn it around at the 2021 Italian Open where he qualified by defeating two top 100 players in Alexei Popyrin and Yoshihito Nishioka.

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.

He had a successful grass court swing, reaching a semifinal and a final at back-to-back challengers in Nottingham, United Kingdom.

[10] 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.

[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.

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.

Majchrzak then received a wildcard to compete at the 2024 BW Open, marking his return to the ATP Challenger Tour.

In February, he was nominated for the Polish Davis Cup team, winning a dead rubber against Maxim Shin of Uzbekistan.

He defeated Bogdan Bobrov, Juan Pablo Paz, Calvin Hemery and Max Houkes en route to his first Challenger final since 2022.

[25][26] He competed again in the second Rwanda Challenger where he came through qualifying to extend his winning streak at the tournament to 10 matches, defeating Ivan Gakhov, David Pichler and Stefan Kozlov to reach his second consecutive semifinal.

He defeated the likes of Ergi Kırkın, Dmitry Popko, Jérôme Kym and Henrique Rocha on route.

During this tournament, he defeated former top 10 player Pablo Carreño Busta on route to the semifinals where he lost to compatriot Maks Kaśnikowski after suffering from a mid-match wrist injury.

He defeated American wildcard Michael Zheng[30] and Daniel Elahi Galán to reach the final round of qualifying where he ultimately then lost to the in-form Mattia Belucci.

At the 2024 Saint-Tropez Open he defeated former top 100 player Borna Gojo, Harold Mayot, and Matteo Martineau to reach the semifinals.

In October, Majchrzak won his third title of the year at the 2024 JC Ferrero Challenger Open in Villena, Alicante Province, Spain.