코스트유크, 마르타

2015–2017

In December 2015, Kostyuk won the "14-and-under" competition at the Junior Orange Bowl in Florida. The following month, she won the 2016 Petits As in Tarbes, France, in both singles and doubles (with Kamilla Bartone).

In January 2017, Kostyuk won the girls' singles title at the Australian Open, defeating Rebeka Masarova in the final. In May, she won an ITF tournament in Dunakeszi (Hungary) without dropping a set, becoming the youngest Ukrainian to win a professional singles title. In September, Kostyuk and Olga Danilović won the girls' doubles title at the US Open. In October, she won the year-end junior girls tournament, the ITF Junior Masters in Chengdu, China, defeating Kaja Juvan in the final.

On 30 October 2017, Kostyuk achieved a career-high junior ranking of world No. 2.

2018–2019: Major debut, Strasbourg quarterfinal

Kostyuk made her main draw tour-level debut at the Australian Open. Having received a wildcard entry into the qualifying tournament, she defeated Arina Rodionova, Daniela Seguel and Barbora Krejčíková to become the first player born in 2002 to play in a Grand Slam tournament main draw. By defeating Peng Shuai in the first round, Kostyuk became the youngest player to win a main-draw match in Melbourne since Martina Hingis in 1996. In the second round, she defeated Australian wildcard Olivia Rogowska in straight sets. In doing this, she became the youngest player to reach the third round of a Grand Slam event since Mirjana Lučić-Baroni reached the same stage at the 1997 US Open. However, she fell in round three to fourth seed and compatriot player Elina Svitolina.

Kostyuk won the Burnie International, a $60k tournament in Australia, in February 2018, and reached the final of the Zhuhai Open in March, also a $60k event, but did not sustain her level of success in the rest of the year.

In 2019, she won two further ITF Circuit titles, and reached the quarterfinals of the WTA Tour event at Strasbourg as a qualifier where she lost to fourth seed Caroline Garcia.

She finished the season ranked No. 155.

2020: US Open third round, French doubles quarterfinal

In February, Kostyuk won the $60k Cairo Open. She also won the doubles tournament in Cairo, playing with Kamilla Rakhimova. Following the break in the season caused by the COVID-19 pandemic, she competed in the Palermo Ladies Open qualifying, reaching the second round, and came through the qualifying to enter the main draw of the Prague Open.

At the US Open, she beat former top-10 player Daria Kasatkina, in straight sets in the first round. She then beat former semifinalist and 31st seed Anastasija Sevastova. In the third round, she met former champion and world No. 9, Naomi Osaka. She overcame a first set deficit by winning the second in a tie-breaker, but was beaten in the third.

2021: First WTA 500 semifinal, top 50

At the WTA 500 Abu Dhabi Open, she reached the semifinals defeating Lucie Hradecká, Hsieh Su-wei, Tamara Zidanšek and Sara Sorribes Tormo.

At the French Open, she defeated former French Open champion and 12th seed, Garbiñe Muguruza, in the first round, 6–1, 6–4. In the fourth round, her best Grand Slam showing, she was defeated by the defending champion, Iga Świątek. Kostyuk reached the top 50 on 1 November 2021, her best career ranking.

2022: Second Australian Open third round

At the Australian Open, she reached the third round defeating 32nd seed Sorribes Tormo, before losing to world No. 6, Paula Badosa.

At the Eastbourne International, she defeated seventh seed Barbora Krejčíková to reach the third round.

She reached the semifinals at the Championnats de Granby where she lost to Daria Saville, after withdrawing from the match.

2023: Major doubles semifinal and WTA Tour title, top 35

At the WTA 500 Adelaide International 1, she went through qualifying and on to the quarterfinals, beating reigning Wimbledon champion Elena Rybakina en route. She defeated 28th seed Amanda Anisimova and Olivia Gadecki to reach the third round at the Australian Open for the third time. In doubles at the same tournament, she reached the semifinals partnering Elena-Gabriela Ruse where they lost to eventual champions Barbora Krejčíková and Kateřina Siniaková.

She reached her second quarterfinal in Hua Hin, Thailand. At the Dubai Championships, after receiving a wildcard, she lost in the second round to eighth seed Belinda Bencic in the second longest match of the season, in 3 hours and 27 minutes.

She reached her third quarterfinal of the season at the inaugural ATX Open in Austin, Texas defeating Dalma Gálfi and Madison Brengle. Next, she defeated Anna-Lena Friedsam to reach the semifinals and forth seed American, Danielle Collins, to reach her first WTA Tour final. She won her maiden title defeating another first time WTA Tour finalist, Varvara Gracheva. She did not shake her Russian opponent's hand, and dedicated her win "to Ukraine and to all the people who are fighting and dying right now". This win lifted her into the top 40 in the singles rankings.

At the Miami Open, Kostyuk won her first-round match against Elisabetta Cocciaretto but was defeated by Anastasia Potapova in the second, and once again refused to shake her opponent's hand.

Despite a first-round loss at the French Open, she reached No. 35 in the rankings. At Wimbledon, she reached again the second round for a third consecutive year, defeating world No. 8, Maria Sakkari, for her first top 10 win. Following the tournament, she brought on Sandra Zaniewska as a coach.

2024: First major singles quarterfinal and top 3 win, top 20

At the Australian Open, she defeated Claire Liu, 25th seed Elise Mertens, Elina Avanesyan and another Russian, qualifier Maria Timofeeva to reach the quarterfinals of a major for the first time. It marked the first time multiple Ukrainian women have reached the third round, and also a record-breaking number of two of those players made it to the quarterfinals at a Grand Slam event in the Open Era. As a result, she reached the top 30 in the rankings.

At the San Diego Open, she stunned top seed Jessica Pegula to reach her first WTA 500 final, with her first top-5 win. Seeded 31th at Indian Wells, she reached the quarterfinals of a WTA 1000 for the first time defeating Mai Hontama, seventh seed Markéta Vondroušová by walkover, 22nd seed Anastasia Pavlyuchenkova and 28th seed Anastasia Potapova, all in straight sets, to reach the semifinals. She reached a new career-high ranking of No. 26 on 18 March 2024.

At the start of the clay-court season, at the WTA 500 Stuttgart Grand Prix, she defeated local wildcard Laura Siegemund, and fifth seed Zheng Qinwen, saving five match points to reach the quarterfinals. She defeated third seed Coco Gauff on her eighth match point, her first top-3 win, to reach the semifinals. Finally, she entered her second WTA 500 final with a straight-sets win over another Grand Slam champion, sixth seed Markéta Vondroušová, her third top-10 win in three days. As a result, she reached a new career-high ranking of No. 21 in the singles rankings. She lost the final to Elena Rybakina, in straight sets. She reached the top 20 two weeks later, following the 2024 Mutua Madrid Open.