[8][12] Ross began gymnastics when she was three years old in Greenville, South Carolina, and also trained in Richmond, Virginia, before the family settled in Aliso Viejo, California.

[13] In 2005, she began training alongside future Olympic teammate McKayla Maroney at the Gym-Max Academy of Gymnastics under coaches Howie and Jenny Liang.

At the 2008 Junior Olympic national championships, she won the balance beam, floor exercise, and all-around titles and finished second on vault.

[15] In April, she competed at the American Classic in San Diego, California and placed second in the all-around behind McKenzie Wofford with a score of 55.316.

[19] She was then selected to compete at the Junior Pan American Championships in Aracaju, Brazil, alongside Bridgette Caquatto, Aly Raisman, and Sabrina Vega.

[20] Making her international debut,[15] Ross contributed to the team's 14-point victory over Canada in addition to winning the individual all-around title.

[26] At the U.S. Classic in Chicago, Ross placed third behind Wieber and Katelyn Ohashi in the all-around and had the highest score on the balance beam.

[28] She then fell off the uneven bars on day two, but she finished strong on the balance beam to win her second straight junior all-around title.

She and teammates Sabrina Vega, McKayla Maroney, Gabby Douglas, Brenna Dowell, and Sarah Finnegan beat silver medalist Canada by nearly 20 points.

[31] In the event finals, she won the silver medal on the floor exercise behind Maroney and placed sixth on the uneven bars.

She and teammates Katelyn Ohashi, Madison Kocian, Lexie Priessman, Elizabeth Price, and Ericha Fassbender won the team event over Russia by more than ten points.

She struggled on the first day of competition, falling on a double pike on floor exercise and her Amanar vault was devalued to a double-twisting Yurchenko.

[37] Because her 16th birthday fell within the calendar year, Ross became a senior elite gymnast in 2012 and was eligible to compete at the Olympic Games.

However, she competed a lower-difficulty vault at the recommendation of the national team coordinator Márta Károlyi and stepped out of bounds on the floor exercise.

[60] In March, she was chosen to participate in the U.S. European tour team to compete in the City of Jesolo Trophy and the USA-Germany-Romania Tri-Meet in Chemnitz, Germany.

[68] There, she won the all-around silver medal behind Biles,[69] and she received the Longines Prize for Elegance along with male gymnast Kohei Uchimura of Japan.

[76][77] In August, Ross competed at the U.S. Classic, where she finished first on balance beam, second in the all-around behind Simone Biles and on floor exercise, and third on uneven bars.

[79] On September 17, Ross was selected to compete at the 2014 World Championships in Nanning, China, alongside Biles, Alyssa Baumann, Madison Kocian, Ashton Locklear, and MyKayla Skinner.

[85] Ross signed the National Letter of Intent to the Bruins on April 15, 2015, but deferred her enrollment until the 2016–17 season to focus on qualifying for the 2016 Summer Olympics.

[86] Ross began the 2015 season at the City of Jesolo Trophy and helped the United States win a team gold medal despite her falling on the floor exercise.

[89][97][98] Ross began attending the University of California, Los Angeles in the fall of 2016 and joined the UCLA Bruins gymnastics program.

[99] Her collegiate debut came on January 7, 2017, in a home meet against Arkansas where she placed first on the uneven bars, third on vault, and eighth on balance beam.

[108] By earning these two national titles, Ross made history as the first female gymnast to become an Olympic, World, and NCAA Champion.

[110] Ross scored a career-high 39.700 in the all-around to help UCLA win the Metroplex Challenge against LSU, Washington, and North Carolina State.

In the Super Six, Ross contributed scores of 9.9875 on balance beam and 9.950 on uneven bars to help UCLA win its first national team title since 2010.

[114][115] Ross helped UCLA win its first meet of the season, the Collegiate Challenge, by tying her career-high all-around score 39.700 and receiving a perfect 10 on the uneven bars.

[122] Then on March 16, Ross completed a "Gym Slam" after earning her first-ever perfect 10 on floor exercise in a win against Utah State.

Then in the finals, Ross earned perfect 10s on the uneven bars and balance beam and UCLA qualified for the NCAA Championships.

[135] Then on January 18, Ross received a perfect 10 on uneven bars for the second meet in a row at a tri-meet against BYU and Utah State.

[151] On August 16, 2018, Ross came forward as a survivor of Larry Nassar's sexual abuse alongside fellow Olympian and UCLA teammate Madison Kocian.