After playing extensively at the under-17 and under-20 level, Swanson debuted for the USWNT in 2016 at age 17, becoming the team's youngest player since Heather O'Reilly in 2002.

Swanson elected to forego her college career at UCLA to turn professional in 2017, signing with the Washington Spirit, where she stayed for three seasons before playing at Sky Blue FC.

[4] Growing up, Swanson considered her older sister Brianna a role model and cites her as a reason she got started in soccer.

[9] Later that week, her father said the reports were false and that Swanson would join the Bruins of the University of California, Los Angeles for the 2016 season as originally planned.

[10] In July 2016, it was announced she delayed entrance to UCLA until January 2017, due to national team commitments for the Rio Olympics and the 2016 FIFA U–20 Women's World Cup.

[11] She appeared in three non-competitive spring scrimmages in early 2017 before departing UCLA prior to starting her freshman season to pursue a professional career.

Swanson recorded her first professional brace later in the season on September 30, 2017, against Seattle Reign FC, where she also became the first teenager in NWSL history to score multiple goals in a single regular-season match.

[21] She made her Sky Blue debut on September 5, 2020, in an NWSL Fall Series match against her former club, the Washington Spirit, entering the game in the 61st minute.

[28] In 2011, Swanson attended the annual United States under–14 girl's national team identification camp from July 13 to August 7 in Portland, Oregon.

[29] Swanson was then called into the U–14 national team training camp at Home Depot Center in Carson, California, from September 18 to 25.

[34] She then moved up to the U–17 national team and traveled to San José, Costa Rica for an international tournament in late April.

[37][38] In late September 2013, Swanson was named to the roster for the 2013 CONCACAF U–17 Women's Championship held in Jamaica from October 30 to November 9.

In preparation for the 2014 FIFA U–20 Women's World Cup in August, the U–20 team also trained in May and July, with a trip to Europe in June.

[49] In the team's second group match against Brazil on August 8, Swanson suffered a right ankle injury in the 27th minute and was replaced by Taylor Racioppi.

[60] The United States qualified for the 2016 FIFA U-20 Women's World Cup after defeating Honduras in the semifinal on December 11.

[65] In the second group stage game against New Zealand the United States won 3–1, Swanson scoring and receiving player of the match honors.

[72] She made her third appearance for the team in their second match of the tournament, coming in for Ali Krieger in the 75th minute to help the USWNT defeat Mexico 1–0.

In the 60th minute, Swanson sent a cross towards Alex Morgan, but it was deflected off Puerto Rican defender Ashley Rivera and into her own net.

[74] Swanson started in the semifinal match against Trinidad and Tobago on February 19, helping the USWNT qualify to the 2016 Olympic Games in Rio de Janeiro after a 5–0 victory.

[81] On April 6, Swanson scored her second international goal off an assist by Carli Lloyd in the team's first match against Colombia.

[87] On July 12, 2016, Swanson was named to the 18–player team that would represent the United States at the 2016 Olympic Games in Rio de Janeiro.

[84] In October Swanson sustained a hamstring injury during a match against the South Korean national team when the USWNT was winning 3–1.

The United States won 3–0, Swanson assisting the third goal scored by Christen Press who was being honored that game for 100 national team caps.

[98] Swanson scored the first goal of the year for the United States in a 3–1 loss against France played at Le Havre.

[101] Swanson also scored against Mexico in the final send off series game for the United States before the 2019 FIFA Women's World Cup.

[105] In their third and final game of the tournament against Japan, the United States won 3–1, Swanson assisting a goal scored by Lindsey Horan.

[108] However, injury and inconsistent play meant she did not see the field for the United States until later that year, in a series of friendlies in September and October versus Paraguay and the South Korean national team.

Her goal against Uzbekistan on April 12 marked a four-match scoring streak, overtaking the record from 2021 previously held by Megan Rapinoe.

[115] During the 2022 CONCACAF W Championship, Swanson played in her 75th national team cap for the United States, the 49th player to do so and the youngest since Heather O'Reilly in 2008.

[123][124] In what was her 100th international appearance, she scored the 57th-minute winning goal to defeat Brazil 1–0 in the Olympic final, earning a gold medal.