Encouraged by her mother, Sybil Smith, a former All-American swimmer at Boston University, and late stepfather, Sheldon Smith, Stephens learned to play tennis at age 9. She reached a career-high junior world ranking of No. 5 before beginning her professional career in 2009. The promise that she had shown as a junior surfaced in 2011 when she reached her career-high doubles ranking of No. 94.

Two years later, Stephens defeated Serena Williams in the quarterfinals of the 2013 Australian Open before losing in the semifinals. She also reached the Wimbledon quarterfinals and advanced to the fourth round of Roland-Garros and the US Open that same year. From 2012 to 2014, Stephens was a member of the U.S. Fed Cup Team. In 2017, she joined the American team for the Fed Cup final. Stephens was defeated by Aryna Sabalenka in three close sets. In 2016, Stephens represented the United States at the Rio Olympics.

Stephens sees the US Open as her special memory box where she has stored the saddest and most joyous moments of her life. Her most painful moment occurred while competing in the 2009 US Open Junior Championships when a relative informed her that her father, John, a former NFL running back, had died in an automobile accident. Her happiest time came eight years later when she held the winner’s trophy in Arthur Ashe Stadium as the 2017 US Open Women’s Champion.

The 2017 US Open was Stephens’ first Grand Slam title. There, she defeated her good friend Madison Keys in the final 6-3, 6-0. “I didn’t think I would ever regroup here [after my dad died],” Stephens told Sports Illustrated. “If someone told me … that I would end up winning the US Open years later, I would’ve been like, ‘You’re crazy.’ I’ve had so many great moments and so many sad moments here.”

At the 2018 Miami Open, Stephens defeated three top 10 players, Garbine Muguruza, Angelique Kerber, and Jelena Ostapenko, on the way to the title. She reached the Roland-Garros final two months later, losing to No. 1 Simona Halep. Stephens rose to a career-high world ranking of No. 3 that year. After a few years of struggling to find her form, she won her first WTA title in several years, claiming the Abierto Zapopan title in February of 2022. 

In addition to tennis, Stephens is passionate about her charitable organization, the Sloane Stephens Foundation. Stephens established the organization in 2013 with the mission of using tennis and education to improve the lives of those experiencing the effects of poverty, health inequity, and educational underdevelopment. The Sloane Stephens Foundation provides several programs to the youth that include Love, Love Compton—its main program—as well as others, such as a summer camp and ACT/SAT tutoring. The foundation has partnered with Soles4Soles as well, which gives gently used shoes to those in need throughout the world. In 2025, Stephens took home the Muhammad Ali Humanitarian Award at the ESPYS.

Stephens has also been an advocate for reproductive health and education on the WTA Tour. Stephens has been leading the way in conversations surrounding the difficulties women on the WTA Tour face when starting families. A tennis player’s career can expand well into their thirties, making the prospect of motherhood challenging for most women. Stephens has been open about the process of freezing her eggs and the alternative options available for women athletes hoping to start a family. Through her openness, Stephens hopes to broaden the conversation on fertility and provide education to fellow players on family planning resources.