Marta Olehivna Kostyuk (Ukrainian: Марта Олегівна Костюк [ˈmɑrtɐ koˈsʲtʲuk]; born 28 June 2002) is a Ukrainian professional tennis player. She has career-high rankings by the WTA of No. 10 in singles, achieved on 14 September 2026, and No. 27 in doubles, reached in May 2023. Kostyuk has won three WTA Tour singles titles, including a WTA 1000 event at the 2026 Madrid Open, and two titles in doubles. Her best performance at the majors is reaching the semifinals of the 2026 French Open and the 2026 Wimbledon Championships. She is currently the No. 2 player from Ukraine.
Kostyuk is the daughter of Oleh Kostyuk and Talina Beiko. Her father was the technical director of the Antey Cup, a junior tennis tournament in Kyiv; her mother was a professional tennis player who reached a career-high WTA ranking of No. 391, won a $10k title in her home city of Kyiv in 1994, and represented a Ukrainian tennis team. Kostyuk is the younger sister of Mariya Kostyuk, who competed for Chicago State University and Southeast Missouri State University, and a cousin of professional football players Vadym and Miro Slavov and gymnast Oksana Slavova.
Kostyuk started playing tennis at a young age at the Antey Tennis Club, on the west side of Kyiv, coached by her mother. She described her initial experience in tennis at age five: "My mom was always working a lot as a coach, and the first time I went to the courts to train, I just understood that if I started doing tennis, I'd get to spend more time with my mom. So that was kind of my motivation – if I played tennis, I'd be around her more often". She was also coached by her maternal uncle Taras Beiko, who had played for the USSR and Ukraine in the late 1980s and early 1990s.
In March 2023, Kostyuk announced her engagement, and in November 2023, she married her fiancé Hryhoriy.
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: Australian Open third round at 15
Kostyuk made her main-draw major-level debut at the 2018 Australian Open, having received a wildcard into the qualifying tournament, where she defeated Arina Rodionova, Daniela Seguel and Barbora Krejčíková to become the first player born in 2002 to play in the main draw of a Grand Slam tournament and the youngest player (at 15 years and 6 months) to qualify for a major main draw since Sesil Karatantcheva at the 2005 Australian Open.
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 major 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 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.
In 2019, she reached the quarterfinals of the WTA Tour event at Strasbourg as a qualifier losing to fourth seed Caroline Garcia She finished the season ranked No. 155.
2020–2021: First WTA 500 semifinal, top 50
Kostyuk came through the qualifying to enter the main-draw of the 2020 Prague Open, losing to Camila Giorgi in the first round.
At the 2020 US Open, she defeated Daria Kasatkina and 31st seed Anastasija Sevastova. In the third round, she met former champion and world No. 9, Naomi Osaka. Kostyuk overcame a first set deficit by winning the second in a tie-breaker, but was beaten in the third.
At the WTA 500 2021 Abu Dhabi Open, she reached the semifinals defeating Lucie Hradecká, Hsieh Su-wei, Tamara Zidanšek and Sara Sorribes Tormo, before her run was ended by Veronika Kudermetova.
At the 2021 French Open, she defeated former French Open champion and 12th seed, Garbiñe Muguruza, in the first round and went on to reach the fourth round, her best major showing to this point, where she was defeated by defending champion, Iga Świątek.
Kostyuk reached the top 50 on 1 November 2021, her highest career singles ranking, thus far.