Siniaková was born to a Czech mother Hana, an accountant,[2] and Russian father Dmitry Siniakov, a former boxer and her coach.

She passed qualifying defeating Mandy Minella and Alexa Glatch, but then lost a three-set encounter with Garbiñe Muguruza in the first round of the main draw.

[10] In November 2013, she reached her first major ITF final at the $75k Sharm El Sheikh event in doubles, but lost alongside Anna Morgina.

[8] At the 2014 Australian Open, she made her major debut, after passing qualifying but then lost to Zarina Diyas in the first round of the main draw.

Nearly after that, she reached her first WTA doubles final at the Silicon Valley Classic alongside Paula Kania, but they lost to Garbiñe Muguruza and Carla Suárez Navarro.

In March 2015, she won her first WTA 1000 match at the Premier Mandatory-level Indian Wells Open, defeating another Russian player, Evgeniya Rodina.

[10] Siniaková started slowly into the 2016 season, but then shone at the French Open, where she reached semifinals in doubles alongside Barbora Krejčíková.

However, during that period, she had success in doubles where she reached the final of Indian Wells and the Premier-level Charleston Open alongside Lucie Hradecká.

Alongside Lucie Hradecká, she did not drop a singles set on the way to the final, but then they lost to Latisha Chan and Martina Hingis.

[9] Siniaková started year well, playing at the Shenzhen Open where she reached the finals in both singles and doubles, but lost to Simona Halep in both.

[9][30] In November, Siniaková won two matches, including the decisive third, as the Czech Republic defeated the USA 3–0 to win the Fed Cup final.

[9] There was a positive start to 2021, when Siniaková and Krejčíková reached the doubles final at the Australian Open, before losing to Elise Mertens and Aryna Sabalenka.

[44][9] At the delayed Tokyo Olympics, Siniaková and Krejčíková won gold in women's doubles, defeating the Swiss pair of Belinda Bencic and Viktorija Golubic in the final.

[49] On home soil, she reached the quarterfinals of the Prague Open in July, being beaten heavily by her doubles partner Krejčíková who would go in to take the title.

[58] At the same tournament in doubles, she reached the final with Krejčíková[59] and won the title for a second time at this major defeating top seeds Elise Mertens and Zhang Shuai, in straight sets.

[60] After poor results in singles, Siniaková dropped down to play an ITF tournament in Poland in August, which she won beating Magda Linette.

[61][62] Siniaková followed up this success in doubles a week later, with her third singles title at the Portorož Open in Slovenia, defeating 2022 Wimbledon champion Elena Rybakina in the final, in three sets.

[64] She had another good win in singles to beat top-20 player Haddad Maia in the first round of the last WTA 1000 of the year at the Guadalajara Open[65] and made the semifinals in doubles alongside Krejčíková.

[66] Siniaková began season at the 2023 Adelaide International 1 where she failed to qualify in singles, but teamed up with Storm Hunter to reach the final in which they were defeated by Taylor Townsend and Asia Muhammed.

[69] She reached her first singles final of the season at the Bad Homburg Open and second at this tournament, defeating second seed Liudmila Samsonova and Emma Navarro in the same day.

[48][9] At the Qatar Open, she defeated Donna Vekić[76] and second seed Coco Gauff to reach the round of 16,[77] where her run was ended by qualifier Danielle Collins.

[80] At the French Open, with new partner Coco Gauff, she lifted her third trophy at Roland Garros defeating 11th seeds Sara Errani and Jasmine Paolini in the final.

[81] At the same tournament in singles, she reached the second round with a win over lucky loser Dalma Galfi,[82] before losing to wildcard Chloe Paquet in a deciding set tie-break.

30 in singles, Siniaková reached her first quarterfinal for the season as a qualifier at the 2024 Berlin Ladies Open defeating Emma Navarro[84] and sixth seed Zheng Qinwen.

[88][89] Siniaková reunited with Barbora Krejčíková in the doubles at the Prague Open, winning their first title together on home soil by defeating wildcards Bethanie Mattek-Sands and Lucie Šafářová in the final as they warmed up for the 2024 Summer Olympics.

[93][94] Going into the Guangzhou Open in October as top seed, Siniaková reached the semifinals with wins over Petra Martić,[95]Alycia Parks[96] and Bernarda Pera.

[104] Partnering Taylor Townsend, Siniaková claimed her 10th major doubles title by winning the Australian Open, defeating Hsieh Su-wei and Jeļena Ostapenko in the final.

[105][106][107] In her next tournament, the 2025 Upper Austria Ladies Linz, she played alongside Zhang Shuai from China and reached the semifinals, where they lost in three sets to Luisa Stefani from Brazil and Tímea Babos from Hungary.

[108][109] In February 2017, she was nominated to the Fed Cup team for the first time by the captain Petr Pála as she was the third best ranked woman Czech tennis player (considering Petra Kvitová's injury) after Karolína Plíšková and Barbora Strýcová and would benefit from the experience.

[111] Siniaková was also part of the Czech team at the 2020-21 Billie Jean King Cup Finals in Prague, where she played doubles alongside Lucie Hradecká.