Born in Moscow, known as Sonya, Sofia Kenin moved to USA when she was a young child. Residing
in Pembroke Pines, Florida, where she was home-schooled, as a junior she reached the singles final at the 2015 US Open (l. Galfi), the semifinals at the 2016 US Open and the quarterfinals at 2016 Wimbledon. She climbed as high as No.2 in the ITF World Junior Rankings representing the United States at the 2014 Youth Olympic Games and competed at the 2016 ITF Junior Masters, both held in China.
Kenin made her Grand Slam main draw debut at 2015 US Open as a wildcard, received for being crowned USTA Girls’ 18s national champion, but fell in the first-round to Duque Mariño.
She also played 2016 US Open as a wildcard, granted for winning USTA Pro Circuit US Open wildcard challenge, losing to eventual R-Up Karolina Pliskova. In 2016, she also lifted titles at $25k ITF event in Wesley Chapel and $50k ITF tournament in Sacramento, finishing the season ranked No.212 (up from No.620 in 2015).
She compiled a 47-28 record at all levels in 2017, finishing at a career-high No.113. In what was only her fourth tour-level main draw appearance, she reached the third-round at US Open as a wildcard (l. Sharapova), after winning the Wild Card Challenge. In Flushing Meadows, she posted the first Top 50 win of her career against No.34 Davis. Also in 2017, she won the $60k ITF title in Stockton, finished R-Up at $60k ITF tournament in Lexington, and reached the semifinals at $60k ITF event in Sacramento. In other tour-level appearances in 2017, made the second round in Québec City (l. Safarova) and suffered a first round loss in Charleston (as qualifier, l. Mattek-Sands). She closed the year strongly by reaching the semifinals at three consecutive ITF Circuit events: $80k ITF/Tyler, $80k ITF/Waco, $25k ITF/Norman.
In 2018 she started the season by reaching her maiden WTA quarter-final in Auckland (l. eventual runner-up Wozniacki). She notably reached the second-round at Indian Wells that made her break into the Top 100 for first time on March 19 (at No.94). After that result, she made a third-round exit in Miami (l. Kvitova) after achieving her best win-by-rank of her career, a three-set victory over No.11 Kasatkina in the second-round.