High school career

Margalis graduated from Countryside High School, where she was also a club swimmer for Saint Petersburg Aquatics. There, she was coached by Fred Lewis. In high school swimming, she was a three-time state champion and held the state record in the 200-yard IM. For four years in a row, Margalis was named her teams’ MVP. Proving her versatility, she also swam the 500-yard free in 2009 in which she also won a state championship. After her performances that season, she was named the 2009-2010 Pinellas County Female Athlete of the Year. That same year, she was named to the National Youth Championship Team.^[2]

College career

Margalis helped the Georgia Bulldogs swimming and diving women's team at the University of Georgia win the NCAA Division I women's team title in 2013 and again in 2014.^[3]

2013

Margalis won gold in the 4x200-meter freestyle relay as a member of the preliminary team and bronze in the 200-meter individual medley at the 2013 World University Games in Kazan, Russia.

2014

At the 2014 National Championships, Margalis won the 200-meter IM and finished third in both the 400-meter IM and 200-meter breaststroke to earn a roster spot on the Pan Pac team — she finished 12th in the 400-meter IM and ninth in the 200-meter IM. Later that year she also competed at the 2014 FINA World Swimming Championships (25 m), swimming the IM events. She won a bronze in the 200-meter IM and finished sixth in the 100-meter IM.^[2]

2015

At the 2015 World Aquatics Championships in Kazan, Russia Margalis swam a 2:10.41 to finish 7th.^[2]

2016

At the 2016 Summer Olympics in Rio de Janeiro, Brazil Margalis won the gold medal with the U.S. women's 4x200-meter freestyle relay team.^[4][5]

2017

At the 2017 World Aquatics Championships Margalis had a strong swim in the 200-meter IM, but could not hold off the final 50 surge of US teammate Madisyn Cox, and finished fourth. In 4x200-meter freestyle relay, Leah Smith led off for the Americans in a personal best 1:55.97. Mallory Comerford (1:56.92) and Margalis (1:56.48) took over the middle legs of the relay as they battled down the stretch with China and Russia. It was a very tight race with China going into the final leg, but Katie Ledecky took off with a 1:54.02 split to help the Americans strike gold again.

At the 2017 Winter Nationals Championships Margalis had a busy weekend as she competed in five individual events and managed to grab three individual titles. She broke the Championship Record in the 200-yard IM with the time of 1:52.63 and finished first in 400-yard IM and 100-yard breaststroke.^[2]

2018

At the 2018 Pan Pacific Swimming Championships Margalis secured a silver medal in the 400-meter IM with a time of 4:35.60.

At the 2018 FINA World Swimming Championships (25 m) Margalis earned the silver medal in the 400-meter IM, turning in a career-best time of 4:25.84 in the event finals. She was also runnerup in the 200-meter IM (personal best 2:04.62) and finished fourth in the 100-meter IM, clocking a 58.32, just .21 of a second off the podium. Margalis was a part of two medal winning relay teams, earning gold in the 4×100-meter medley relay and silver in the 4×200-meter freestyle relay.^[2]

2019