Hamm competed in four FIFA Women's World Cups: the inaugural 1991 tournament in China, 1995 in Sweden, 1999 and 2003 in the United States.

While living in Florence, Italy, Hamm first played soccer, which was hugely popular there; her entire family quickly became involved in the sport.

[14] Hamm played sports from a young age and excelled as a football player on the boys' team at junior high school.

[18][19] From 1989 to 1993, Hamm attended the University of North Carolina at Chapel Hill, where she helped the Tar Heels win four NCAA Division I Women's Soccer Championships in five years.

[23] Hamm was a member of the United States women's national college team that won a silver medal, being defeated by China in the final, at the 1993 Summer Universiade in Buffalo, New York.

[36] Hamm finished her club career as a WUSA champion when the Freedom defeated the Atlanta Beat 2–1 in overtime to win the Founders Cup on August 24, 2003.

[42] She and teammates Foudy and Fawcett were honored with a pre-game ceremony where they were presented with framed jerseys and roses in front of 15,549 fans at Home Depot Center in Carson, California.

[45] She competed in four FIFA Women's World Cup tournaments: the inaugural 1991 in China, 1995 in Sweden, 1999 and 2003 in the United States.

She led the team at three Olympic Games, including: 1996 in Atlanta (the first time women's soccer was played), 2000 in Sydney, and 2004 in Athens.

In 1991, Hamm was named to the roster for the inaugural FIFA Women's World Cup in China under North Carolina coach Anson Dorrance.

Goals from Kristine Lilly and Tiffeny Milbrett led to a 2–0 win for the U.S. Hamm played goalkeeper for a few minutes after Briana Scurry received a red card and was removed from the match.

[66][67] Although she was carried off by stretcher in the final minute,[68] her team won their first Olympic gold medal with a 2–1 win witnessed by 76,481 fans in the stadium – the largest crowd for a soccer event in the history of the Olympics and the largest crowd for a women's sports event in the United States.

[73] The following month, she led the national team at the 1999 FIFA Women's World Cup, hosted by the United States.

[74] During the team's first group stage match against Denmark, she scored her 110th international goal and served an assist to Julie Foudy as the U.S. won 3–0.

[78][76] During the team's final group stage match, head coach Tony DiCicco rested a number of players, including Hamm, who was substituted at half-time.

The five American players to take penalty kicks, including Hamm, converted; China missed one attempt so that the home team won.

[31] After 12 hours of sleep, she joined the team for magazine cover shoots, went to Disneyland for a celebration rally, and made numerous television appearances.

[91][89] Originally scheduled for China, the 2003 FIFA Women's World Cup was moved to the United States due to the SARS outbreak.

[95] She scored twice against Nigeria and served the assist for the team's third goal to lead the U.S. to a 5–0 win and qualification for the quarter-finals with one match to play.

[102] Hamm helped lead the U.S. national team to its second gold medal at the 2004 Summer Olympics in Athens and was selected by her fellow Olympians to carry the American flag at the closing ceremony.

[107] During the semi-final match against Germany, Hamm served an assist to Heather O'Reilly who scored in overtime to secure a 2–1 win.

[109] The game marked the last Olympic appearance for the five remaining players who had helped win the inaugural 1991 FIFA Women's World Cup: Hamm, Julie Foudy, Joy Fawcett, Brandi Chastain, and Kristine Lilly (often referred to as the Fab Five).

[109] Regarded as one of the greatest female soccer players of all time,[110][111][112][113] Hamm was an athletic, dynamic, and technically gifted striker, renowned for her speed, skill, footwork, stamina, and ability on the ball, as well as her consistency.

[120][121][122] She married then-Boston Red Sox shortstop Nomar Garciaparra on November 22, 2003, in Goleta, California, in a ceremony attended by a few hundred guests.

[14][127][128] Dedicated to promoting awareness of and raising funds for families in need of a bone marrow or cord blood transplant, the foundation encourages people to register in the national bone marrow registry and provides funds to UNC Health Care and Children's Hospital Los Angeles.

[129] During her time as an international soccer player, she signed endorsement deals with Gatorade, Nike, Dreyer's Ice Cream, Pepsi, Nabisco, Fleet Bank, Earthgrains, and Powerbar.

[31][134] She co-starred with Michael Jordan in a popular television commercial for Gatorade in the spring of 1999 which featured the two athletes competing against each other in a variety of sports while the song Anything You Can Do (I Can Do Better) is heard.

She received a 93 overall rating, tied for fourth highest among all Icons with Ronaldinho and Johan Cruyff and behind only Pelé, Zinedine Zidane and Ronaldo.

[130][156] She is the author of the national bestseller Go For the Goal: A Champion's Guide to Winning in Soccer and Life and juvenile fiction book Winners Never Quit.

[160] In October 2014, Hamm was announced as a co-owner of the future Major League Soccer team, Los Angeles FC.