CiCi was born in San Francisco to Gordon and Lori Bellis, and grew up in Hillsborough and Atherton in northern California.

As a child, Bellis aspired to go to college at Stanford, but ended up declining a scholarship to turn pro due to her success as a teenager.

Her biggest triumph in the 2013 season was winning Les Petits As in France, a prestigious tournament for juniors between 12 and 14 years old.

Specifically, she won the Copa del Café in Costa Rica, the USTA International Spring Championships and the Easter Bowl in the United States, and the Trofeo Bonfiglio in Italy.

[6] She followed up this success by also reaching the French Open doubles final with Markéta Vondroušová, which they lost in a match tiebreak.

In contrast, Bellis struggled at the three Grand Slam singles events she entered that year, with her best result being a third round appearance at the French Open.

In August 2014, Bellis won the USTA Girls' 18s National Championship, defeating Tornado Alicia Black in the final.

[2][7] Bellis and Black were then both selected to represent the United States at the Junior Fed Cup along with Sofia Kenin.

[2] In her WTA Tour-level debut, she upset 12th seed Dominika Cibulková, who was the runner-up at the Australian Open earlier in the year.

[11] A month after the US Open, Bellis won her first two professional titles in singles in back-to-back weeks, both in South Carolina at the $25k level.

The following month, Bellis qualified for the main draw of the US Open, and improved on her result from two years earlier by reaching the third round, where she lost to the eventual champion Angelique Kerber, in straight sets.

She won her final three tournaments of the year, including two $50k titles in Canada at Saguenay and Toronto, which brought her into the top 100 for the first time.

Bellis was forced to skip the Australian hard-court season in January due to left leg problems with her hip and hamstring.

[13] She played her first main draw of the year at the Dubai Championships, where she made her first Premier 5 quarterfinal and extended her main-draw win streak at all levels to 17 matches.

[14] Bellis played in her first WTA Tour clay-court season and reached quarterfinals at the Rabat Grand Prix in Morocco.

She made another third-round appearance at a Grand Slam tournament at the French Open and became just the third American aged 18-or-under to make it this far at the major in Paris since the turn of the century.

Nonetheless, Bellis won the WTA Newcomer of the Year award for her rankings achievement and her solid performance across all surfaces.

[citation needed] At the 2020 Australian Open, Bellis defeated 22nd ranked Karolína Muchová in the second round, before falling to world No.

[18] Having competed her last match on the ITF Circuit in November 2020 in Charleston, she announced her retirement from professional tennis on Instagram on 19 January 2022.