Olivia Gadecki (; born 24 April 2002) is an Australian professional tennis player. She has a career-high singles ranking by the WTA of No. 83, reached on 7 October 2024, and a best doubles ranking of world No. 64, achieved on 22 July 2024. As of September 2024, she is the Australian No. 1.
Gadecki made her main-draw debut on the ITF Circuit in Brisbane, in September 2016.
In January 2021, Gadecki made the second round of the Australian Open qualifying. She was awarded a wildcard into the Gippsland Trophy, where she made her WTA Tour main draw debut.
In February, Gadecki won her first WTA Tour singles main-draw match at the Phillip Island Trophy. She followed this up with her first top-10 win, defeating the top seed, former Australian Open champion and world No. 4, Sofia Kenin. With Gadecki's career-high ranking being No. 988 in the world, this was Kenin's worst defeat by ranking on the WTA Tour. Gadecki lost in the third round. The following week, she re-entered the WTA rankings at No. 642. In May 2021, Gadecki won her first professional singles title in Turkey.
In August 2021, she won the singles and doubles titles at Vigo, Spain. It was her second singles title and fifth doubles title.
On 20 September 2021, Gadecki debuted in the Australian top 10 in singles and doubles rankings. She ended the year with a singles ranking of No. 238.
Gadecki did not enter the 2022 Australian Open due to the requirement for all players to be vaccinated against COVID-19
In April 2022, Gadecki broke into the top 200, after reaching three finals from four Australian Pro Tour appearances.
She made her debut at the Australian Open as a wildcard and defeated Polina Kudermetova in the first round before losing her next match to Marta Kostyuk. As a result, her ranking climbed to No. 144, on 20 February 2023.
She reached a career-high ranking at world No. 120 on 15 January 2024, prior to the 2024 Australian Open where she received a wildcard for the main draw, losing to Sloane Stephens.
Ranked No. 177, she qualified for the Wimbledon Championships making her debut at this major but suffering a straight sets loss to Robin Montgomery.
Ranked No. 152, she qualified for the WTA 500 Guadalajara Open and defeated Sloane Stephens in the first round. She then upset second seed Danielle Collins, in straight sets in the second round, to reach her first WTA Tour quarterfinal and first at the 500-level. Next, she defeated Martina Trevisan, her third top 100 win, to reach her first WTA Tour semifinal (the third active Australian woman player to reach a semifinal at the WTA 500 level after Ajla Tomljanović and Daria Saville), and finally Camila Osorio to reach her maiden career final. As a result, she reached a new career-high in the top 90, raising close to 65 positions, becoming the Australian No. 1 ahead of Daria Saville in the women's singles rankings on 16 September 2024. She became the first Australian to reach a WTA 500 singles final since Ash Barty in January 2022 in Adelaide. Gadecki lost in the final to Magdalena Fręch.