Beard made her first Olympic appearance at the 1996 Atlanta Olympic Games at the age of 14, while a student at Irvine High School in Irvine, California. She won silver medals in the 100-meter and 200-meter breaststrokes, and a gold in the medley relay. Her young-teen manner captured the attention of the media, and she was often photographed clutching her teddy bear, even on the medal stand. She won a bronze medal in the 200-meter breaststroke at the 2000 Sydney Olympics. Amanda attended the University of Arizona where she captured an individual NCAA National Championship in 2001.

In 2003 she became the world champion and world record holder in the 200-meter breaststroke. She also made a good showing at the 2004 U.S. Olympic Swim Trials, and she competed in the 2004 Athens Olympic Games, where she won a gold medal in the 200-meter breaststroke, her first individual gold medal. She also won a silver medal in the 200-meter individual medley, and she finished fourth in the 100-meter breaststroke.

Beard has won eight United States titles (three times in both the 200m breaststroke and the 100m breaststroke, plus twice in the 200m individual medley). She was first in a world ranking of 200m breaststrokers in 2003.

Her modeling work has included the 2006 Sports Illustrated Swimsuit Edition and a nude pictorial in the July 2007 issue of Playboy. She is a spokesperson for Defenders of Wildlife, and enjoys interior decorating. Both of her sisters, Leah and Taryn, are swimmers. Amanda placed eighth in the Toyota Grand Prix of Long Beach Celebrity car race in 2006.

She recently began own regular segment on the Fox network's popular sports talk program, The Best Damn Sports Show Period.