She played for Manchester United and Arsenal in the English FA Women's Super League as well as Paris Saint-Germain in France.

In 2019, Heath co-founded a lifestyle brand, re-inc, with fellow athletes Christen Press, Megan Rapinoe, and Meghan Klingenberg.

Heath has a younger brother, Jeffrey, and two older sisters, Perry and Katie, who are active in Athletes in Action and Champions for Christ.

[12][13] Heath committed to attend the University of North Carolina (UNC) when she was due to begin her junior year at high school.

[14] In her consensus freshman year in 2006 with the Tar Heels, she was part of the All-America 2006 national championship team and made 23 appearances at left midfield (22 starts), scoring four goals and assisting nine.

She was named to the NCAA All-Tournament Team and also the first runner-up for the MAC Hermann Trophy, given to the college soccer's top player.

UNC soccer coach Anson Dorrance notes that Heath preferred to nutmeg opposing players rather than dribble the ball around them.

The next year she played for Hudson Valley Quickstrike Lady Blues; the team finished the season second in their division and made it to the 2007 Conference Semifinal.

In 2010, she was the first overall pick in the Women's Professional Soccer (WPS) 2010 college draft and was selected by the expansion team Atlanta Beat.

[19] On December 10, 2010, Heath, along with Beat teammates Eniola Aluko and Angie Kerr, were traded to Sky Blue FC in return for the fourth and eighth pick in the 2011 WPS Draft as well as future considerations.

[23] In 2013, Heath signed a six-month contract with Paris Saint-Germain (PSG) in the top-tier French league, Division 1 Féminine, until the end of the season on May 23, 2013.

[26] Heath returned to PSG from the Portland Thorns in September 2013 until June 2014, after she had a sore right foot in the 2013 NWSL Championship.

[29] After completing the season with Paris-Saint Germain, she joined the Thorns in July 2013, helping them attain a third-place finish in the NWSL.

The Thorns won the 2013 NWSL Championship after defeating the Western New York Flash 2–0, with Heath scoring the game-winning goal from a direct free kick.

It was first described as a minor injury that was expected to result in a short spell out of play, with an estimated return date listed as May 27 against the Boston Breakers.

[38] The back injury lasted longer than initially thought, so she was sent to Los Angeles and was treated by her coaching staff.

Heath scored another goal in Portland's 2–1 win over the Seattle Reign in the semi-final, setting up a re-match with the North Carolina Courage in the final.

[47] Heath was named one of five nominees for NWSL Most Valuable Player; her Thorns teammate Lindsey Horan won the award.

[53][54] On September 9, 2020, Manchester United of the FA Women's Super League announced it had signed Heath, along with her national teammate Christen Press, to one-year contracts.

[55] She made her debut on October 4 as a 70th minute substitute in a 3–0 victory over Brighton & Hove Albion, registering an assist.

[64] Having been ruled out for the conclusion of the season with a minor hamstring injury sustained in training, Heath and Arsenal mutually agreed to terminate her contract early on April 28, 2022.

[66] With OL Reign, Heath only played a few matches due to injuries and had a season ending knee surgery in September.

[70] Heath was named the 2009 U.S. Soccer Young Female Athlete of the Year and earned two more caps for the USWNT in 2009, with both appearances coming against Canada in July.

She did not play for the U.S. in 2010 due to an illness and a major ankle injury suffered during the WPS season which required surgery.

In the World Cup final, Heath entered the game in the 116th minute of extra time as a substitute for Megan Rapinoe.

[75] Heath was a regular starter on the USWNT at the 2015 FIFA Women's World Cup in Canada, starting five of the U.S.'s seven games.

Heath was named 2016 U.S. Soccer Female Player of the Year after receiving 40% of the vote, ahead of Crystal Dunn with 34%.

[85] After undergoing ankle surgery in January 2018, Heath made her return to the field on June 12 in a friendly against China, where she scored the match-winner in a 2–1 victory.

[159][160] In June 2022, Heath shared a photo on her Instagram account of a painting she had produced for sale at RE–INC titled Out Now, which depicted the words "I am gay" spelled out in large, multi-colored all caps block letters.