While still attending high school, Lilly became a member of the United States women's national team.

Lilly competed as a student-athlete, playing for the university's North Carolina Tar Heels women's soccer team from 1989 to 1992.

[5] As a senior, she won the Honda Sports Award as the nations's top soccer player.

On August 20, 1995, Lilly joined Washington Warthogs of the now-defunct Continental Indoor Soccer League.

February 2001 saw the formation of the world's first women's professional soccer league in which all the players were paid.

In 2003 Lilly started all nineteen games in which she played, chipping in three goals and four assists and again being named to First Team All-WUSA, the only player in the history of the league to do so.

Following the termination of the league, Lilly followed former Boston Breakers head coach Pia Sundhage to Sweden to play for Damallsvenskan club KIF Örebro DFF in 2005.

On September 16, 2008, Lilly was allocated to Boston Breakers along with USWNT teammates Angela Hucles and Heather Mitts.

The inaugural 2009 Women's Professional Soccer season saw Lilly appear in all twenty games (playing every minute) and score three goals with three assists.

Lilly made her debut for the United States national team in 1987, when she was still attending high school.

During her international career, she surpassed the previous women's world record of 151 caps, held by Norway's Heidi Støre, on May 21, 1998.

[5] On January 30, 1999, she surpassed what was then the men's record of 164 caps, held by Adnan Al-Talyani of the United Arab Emirates.

Unlike several of her longtime teammates (among them Joy Fawcett, Julie Foudy, and Mia Hamm), she did not retire after the team's "farewell tour" which finished on December 8, 2004.

In the same match, she equaled Michelle Akers for second place on the team's all-time goal scoring list with 105.

Her last match for the national team, representing her record 354th cap, was a World Cup qualifying loss to Mexico (1–2) on November 5, 2010, in which she played for six minutes as a substitute.

She is married to Brookline firefighter David Heavey, a former hockey player and golfer at the University of Connecticut.

She appeared in the HBO documentary Dare to Dream: The Story of the U.S. Women's Soccer Team.

Lilly helps run a soccer camp with Mia Hamm and Tisha Venturini-Hoch.

[9] Kristine Lilly competed in five FIFA Women's World Cup: China 1991, Sweden 1995,

USA 2003 and China 2007; and three Olympics: Atlanta 1996, Sydney 2000, and Athens 2004; altogether played in 46 matches and scored 12 goals at those eight global tournaments.