Lia Thomas defeated Olympic medallists Emma Weyant and Erica Sullivan to win the women's 500-yard freestyle event in Atlanta ©Getty Images

Swimmer Lia Thomas made history in the United States by becoming the first transgender athlete to win a National Collegiate Athletic Association (NCAA) Division I title.

Thomas, who was representing the University of Pennsylvania, triumphed in the women’s 500 yards freestyle event yesterday in a time of 4min 33.24sec, beating Olympic medallists Emma Weyant and Erica Sullivan.

University of Virginia swimmer Weyant, who claimed 400m individual medley silver at last year’s Olympics, was 1.75sec behind Thomas in second, while University of Texas' Sullivan, who captured 1,500m freestyle silver at Tokyo 2020, finished third.

Thomas’ participation has caused controversy and the swimmer was reportedly heckled by some spectators when being interviewed after her victory, with one calling her a "cheater" at the Mcauley Aquatic Center in Atlanta.

"I try to ignore [negative comments] as much as I can," Thomas told ESPN.

"I try to focus on my swimming and what I need to do to get ready for my races and block out everything else."

CeCé Telfer was the first transgender athlete to win an NCAA title when she was crowned a Division II track and field champion in 2019 with success in the women's 400m hurdles.

Thomas is expected to line-up in today’s 200 yards freestyle as well as tomorrow’s 100 yards freestyle.

Under NCAA rules, Thomas is allowed to compete in women's events as she has completed the necessary one year of testosterone-suppression treatment.

Thomas competed for two full seasons on the men's team prior to fully transitioning, before switching to the women's in 2021.

Cynthia Millen resigned as an official at USA Swimming last December after 30 years at the national governing body in protest of Thomas participating in the sport.

Millen accused Thomas of "destroying women’s swimming" in an interview with Fox News following her resignation.

Thomas has also received support, with more than 300 current and former NCCA and US Olympic swimmer signing a letter last month defending her inclusion.

Among those included Sullivan who said: "I was fortunate enough to be welcomed with open arms in the swim community when I came out as gay.

"Just with my own personal good experience of coming out and feeling all that love and support within my swim community, I feel like [Lia] deserves the same thing."

An open letter published last month supported Lia Thomas' participation in women's swimming events in the United States ©Getty Images
An open letter published last month supported Lia Thomas' participation in women's swimming events in the United States ©Getty Images

Schuyler Bailar, the first openly transgender NCAA Division I swimmer, added: "The amount of discrimination [Thomas] has experienced, the amount of hatred, the amount of just blatant cruelty that has been projected and targeted at her, it is inhumane.

"It is unkind.

"It is horrible.

"It is really hard to see as another transgender athlete, in person.

"And, to be quite honest and frank with you, it is life-threatening to trans people in general, because we already are at risk."

In January, the NCAA Board of Governors updated its transgender policy, voting in support of a sport-by-sport approach.

The NCAA claims the policy will preserve opportunity for transgender student-athletes while balancing fairness, inclusion and safety for all who compete.

The policy is said to align with the approach taken by the United States Olympic and Paralympic Committee and International Olympic Committee.