Like other precocious rising juniors of her generation, Madison Keys joined the professional tour as soon as she was eligible, her fourteenth birthday. In 2009, she won her first WTA match at Ponte Vedra Beach, Florida. Keys became the seventh-youngest player to win a WTA match.

Thanks largely to an excellent first serve and a blistering forehand, the 5 ft. 10 in. right-hander has been ranked consistently among the top 30. “I can say that she almost matches Serena [Williams] in power,” former professional player Chris Evert once said. “Her power off both sides [forehand and backhand] is tremendous.” Keys was a member of the U.S. Fed Cup Team in 2014, 2016, 2018, and 2019, as well as the U.S. Olympic Team in 2016. She reached her career-high singles rank of No. 7 in October 2016.

Keys captured her second of five WTA titles at the 2016 Birmingham Classic, reaching the fourth round of the four major events. She finished the year with a career-high World No. 7 ranking. Some other notable results at the majors include as a semifinalist at the 2015 Australian Open and the 2018 French Open. Keys was also a quarterfinalist at Wimbledon in 2015. At the 2017 US Open, Keys lost in the final to Sloane Stephens, her close friend. Stephens, the tireless runner, zipped past No. 15 seed Keys, the slugger, 6-3, 6-0. “Sloane is one of my favorite people,” Keys said after the match. “I didn’t play my best tennis, and if there’s someone I have to lose to, I’m glad it’s her.”

As of 2020, Keys has endorsement deals with Nike for a clothing line and with Wilson for racquets. She is also passionate about giving back to others. Keys was a leader in the FearlesslyGiRL organization before founding her own charity, Kindness Wins, in 2020. The organization emphasizes the importance of even small acts of kindness through its four main tenets: support, activate, encourage, and share. Kindness Wins dedicates its efforts to supporting professional athletes and elevating others who align with the organization’s message.

In 2022, Keys made it to a singles ranking of no. 11, winning her 6th title—and first since 2019—at the Adelaide International 2 tournament in Australia. She was also nominated as a member of Team USA at the Billie Jean King Cup tournament. In January of 2023, she participated in the inaugural United Cup tournament in Australia with Team USA. She won all five of her matches and, together with Frances Tiafoe, Taylor Fritz, and Jessica Pegula, captured the title for the United States. Her strong showing at the United Cup launched her to a No. 10 world ranking in January of 2023. She won her 7th title at Eastbourne in July 2023 and finished the season with a semifinal run at the US Open. 

In 2024, Keys won her eighth WTA title in Strasbourg and started 2025 off by winning the title at the Adelaide International. However, her greatest career accomplishment thus far came at the 2025 Australian Open, when she won her first major singles title at 29 years old, defeating reigning two-time champion Aryna Sabalenka. With this title, she became the oldest first-time Australian Open champion in the Open Era and became the first person in 20 years to beat both the world No. 1 and world No. 2 ranked players on her way to the title.  Keys also reached her highest career ranking of No. 5.

In 2025, Keys also broke into the podcasting business, releasing the podcast “Player’s Box” with fellow American players Jennifer Brady, Jessica Pegula, and Desirae Krawczyk. This podcast highlights player experiences on tour while also engaging in fans’ tennis questions.