William Barrett (born 1960) is an American former competition swimmer who won a silver medal in the 200-meter individual medley at the 1982 World Aquatics Championships. In 1980, he won a national title in the same event and set a new world record. He also qualified for the 1980 Summer Olympics in the 100-meter breaststroke, but could not compete because of the United States-led boycott over the Soviet invasion of Afghanistan. The same year, Swimming World Magazine named him the American Swimmer of the Year.
Barrett enrolled in the University of California, Los Angeles (UCLA), and swam for coach Ron Ballatore's UCLA Bruins swimming and diving team in NCAA competition from 1980 to 1982. He was recognized as the Pacific-10 Conference swimmer of the year for three consecutive years.