[12] As a member of the U.S. women's national team, Stewart has won gold medals in the 2016,[13] 2020, and 2024 Olympics[14] and at the 2014, 2018, and 2022 FIBA World Cups.

Due to her height her coaches wanted her inside as a rebounder, but her father encouraged her to practice ball handling skills and a perimeter shooting ability.

[16][19] Stewart attended Cicero–North Syracuse High School (C-NS) in Cicero, where she played for head coach Eric Smith.

As a junior, she helped lead her team to the state AA public school title, with a 22–3 record for the year.

[26] Stewart was selected as a member of the 2012 McDonald's All-American team, which represented the 24 best female high school basketball players.

The selected players were grouped into two squads that competed in the annual McDonald's All-American Game, held that year in Chicago.

The top 20 high school players in the country were named as WBCA All-Americans and were eligible to play in the all-star game.

[30][31] In March 2012, in a surprise presentation by Tamika Catchings, Stewart received the Gatorade National Girls Basketball Player of the Year award.

Although double-teamed, she scored ten points in a 12–0 run that gave C-NS a commanding 23-point lead early in the fourth quarter.

"[18] Stewart signed her commitment letter on the hood of her car, then gave it to her father at his office to fax to the school.

[49] In March 2013, she started early morning sessions with Chris Dailey, associate head coach, to concentrate on shooting and post moves.

Stewart immediately made an impact in the league as she scored 23 points in her debut game against the Los Angeles Sparks.

Her season performance helped lead the Storm back to the playoffs for the first time in 3 years with the number 7 seed in the league, but lost in the first round elimination game to the Atlanta Dream.

On August 6, 2018, Stewart scored a season-high 32 points in a 96–80 victory over the New York Liberty, making it her fourth 30-point game of the season.

In the semi-finals, Stewart started off the series strong with a 28-point performance along with a career-high 6 three-pointers in a 91–87 victory against the Phoenix Mercury in Game 1.

[62][63] Stewart missed the entire 2019 WNBA season after suffering an injury while playing for Russian club Dynamo Kursk in the 2019 EuroLeague Women final on April 14 that was later confirmed to be a torn Achilles.

[65] Because the WNBA currently lacks any kind of inactive list, the Storm suspended Stewart in order to free up a roster spot.

Shortly thereafter, the league made her a paid ambassador for the 2019 season, making her the first active player to fill such a role.

[70] On October 20, 2024, the New York Liberty won its first-ever WNBA Championship in franchise history when it defeated the Minnesota Lynx in a 3-2 Finals series.

[75] In June 2018, Stewart signed with Dynamo Kursk of the Russian Premier League[76] and was later named MVP of the EuroLeague Women regular season.

However, Mike Flynn, director of a prominent Amateur Athletic Union team, persuaded her parents that the invitation was an honor, so they relented.

Stewart helped the team win the gold medal in the First FIBA Americas U16 Championship for Women, held in Mexico City.

Despite playing with college age players, she earned a starting position for all games, and again led the team in points, rebounds and blocks.

She joined future UConn teammates Moriah Jefferson and Morgan Tuck on the 12-player squad that competed in the 2012 FIBA Americas U-18 National Championship, held in August 2012, in Puerto Rico.

[92] Stewart, along with teammates Moriah Jefferson and Morgan Tuck, were three of the twelve players selected to be on the team representing the US at the U19 World Championship for Women held in Klaipėda and Panevėžys, Lithuania, in July 2013.

Only five other players have won this award more than once, Teresa Edwards, Lisa Leslie, Cheryl Miller, Dawn Staley and Diana Taurasi, and none have accomplished this at so young an age.

[96][97][98][99][100][101][102][103] USA Basketball named Stewart to the squad that played at the 2016 Summer Olympics in Rio de Janeiro.

She won the gold medal with Team USA and joined Sheryl Swoopes, Cynthia Cooper-Dyke, Ruth Riley, Tamika Catchings and fellow UConn alums Kara Wolters, Swin Cash, Sue Bird, Diana Taurasi, and Maya Moore, as female basketball players who have won NCAA titles, WNBA Championships, and Olympic gold medals.

[110] Stewart is married to former WNBA and EuroLeague Spanish professional basketball player Marta Xargay Casademont.

In August 2021, about 48 hours after Stewart won an Olympic gold medal in Tokyo, their first child, Ruby Mae Stewart-Xargay, was born via surrogacy.