Born in Selma, Alabama, Mia was the fourth of six children of Bill and Stephanie Hamm. She wore corrective shoes as a toddler after being born with a club foot. Hamm spent her childhood on various United States Air Force bases around the world with her family. While living in Florence, Italy, Hamm first played soccer, which was hugely popular there; her entire family quickly became involved in the sport.

On May 22, 1999, Hamm broke the all-time international goal record with her 108th goal in a game against Brazil in Orlando, Florida. The following month, she led the national team at the 1999 FIFA Women's World Cup, hosted by the United States. 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. Against Nigeria, Hamm's low free kick was knocked into the goal by a Nigerian midfielder. Within a minute, Hamm scored with a free kick. She later served an assist to Kristine Lilly before being substituted in the 57th minute. The U.S. won 7-1 and secured a berth in the quarter-finals. 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 U.S. defeated Korea 3-0 and finished Group A with nine points. In the quarter-finals, the U.S. defeated Germany 3-2. Playing Brazil in the semi-finals, Hamm was knocked down in the penalty area late in the second half; Michelle Akers converted the subsequent penalty and their team won 2-0.  After 90 minutes of scoreless regulation time and 30 minutes of sudden death, the 1999 FIFA Women's World Cup Final was decided by a penalty shootout between the U.S. and China. The five American players to take penalty kicks, including Hamm, converted; China missed one attempt so that the home team won. The final surpassed the 1996 Atlanta Olympic final as the most-attended women's sports event, with more than 90,000 people filling the Rose Bowl in Pasadena, California. It held the record until 2014 for the largest U.S. television audience for a soccer match with 17,975,000 viewers. As of July 2015, it ranks third following the 2015 FIFA Women's World Cup (25,400,000 viewers) and 2014 FIFA World Cup group stage match between the U.S. men's team and Portugal (18,220,000 viewers).  Immediately following the final, Hamm collapsed in the locker room from severe hydration. She was treated by medical staff with an intravenous drip and three liters of fluids. 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. A week later, the team met President Clinton at the White House and flew with Hillary and Chelsea Clinton on Air Force One to Cape Canaveral. Her leadership and performance at the 1999 World Cup cemented Hamm as a soccer icon.

Was she the best player on the team?
Hamm broke the all-time international goal record with her 108th goal in a game