[26] In December 2016, Ledecky was chosen as one of the sponsors of the US Navy aircraft carrier USS Enterprise alongside Olympic gold medal-winning gymnast Simone Biles.

In her third, and first relay event of her international career, the 4×200-meter freestyle, Ledecky and teammates Shannon Vreeland, Karlee Bispo, and Missy Franklin won gold in 7:45.14.

Ledecky began the year by breaking her own world records in the 800- and 1500-meter freestyle at the 2014 Woodlands Swim Team Senior Invitational in June.

Despite being in season and swimming multiple events, Ledecky was able to first break the world record in the 1500-meter freestyle with a time of 15:34.23,[43] bettering her previous mark of 15:36.53.

[46] In the 200-meter freestyle final, Ledecky had over a half-second lead on the field at the halfway point before winning by 1.46 seconds with a meet record time of 1:55.74.

Less than an hour later, Ledecky won the 800-meter freestyle, swimming under her world record pace for most of the race before touching in at 8:11.35, the second-fastest time ever, to win by 7.52 seconds over New Zealand swimmer Lauren Boyle.

[47] The next day, Ledecky added her third meet record by swimming on the American 4×200-meter freestyle relay team with Shannon Vreeland, Missy Franklin, and Leah Smith.

National Team Director Frank Busch described Ledecky's 1500 performance as "the most impressive race I have ever seen, and I've been in the sport for 50 years.... She's blazing a completely different trail than anyone who has come before.

[57] On the fifth day of competition, Ledecky, with Missy Franklin, Leah Smith, and Katie McLaughlin won gold in the 4×200-meter freestyle relay.

[60] Ledecky's first event in the 2016 Summer Olympics was the 4×100-meter freestyle relay, swimming the anchor leg for the United States in both the prelims and final.

Swimming the anchor leg again, Ledecky provided the fastest split of the field (1:53.74) to turn a 0.89-second deficit into a 1.84-second victory, stopping the clock at 7:43.03.

[68] At the Pac-12 Championships in Federal Way, Washington, Ledecky earned Swimmer of the Meet honors with four American records as Stanford won its first conference title in four years.

[69] On the meet's third day, she won the 400-yard individual medley in a new American record of 3:57.68 before finishing second to teammate Simone Manuel in the 200-yard freestyle with a personal best time less than a half hour later.

[70] On the meet's final day, Ledecky joined Manuel, Neal, and Janet Hu to break the NCAA and American record in the 400-yard freestyle relay.

[73] In the meet's final event, Ledecky joined Manuel, Neal, and Hu to swim the second leg of Stanford's 400-yard freestyle relay.

The team lowered its previous record with a time of 3:07.61, securing a 526.5–366 decision over runner-up California-Berkeley, the largest championship margin of victory since 2003.

[74] Following the season, Ledecky became the first freshman in 35 years to receive the Honda Cup, which recognizes the nation's top female collegiate athlete.

[78] On the fourth day of competition, Ledecky tied for silver in the 200-meter freestyle (with Emma McKeon), finishing behind Federica Pellegrini with a time of 1:55.18.

On the fifth day of competition, Ledecky, with Leah Smith, Mallory Comerford, and Melanie Margalis won gold in the 4×200-meter freestyle relay.

[81] A week following Stanford's championship win, Ledecky announced at the National Press Club that she will forego her final two seasons of NCAA eligibility in order to accept professional endorsement and sponsorship opportunities.

On the first day of competition, Ledecky won gold in the 800-meter freestyle with a championship-record time of 8:09.13, topping runner-up Ariarne Titmus of Australia by 7.94 seconds.

The next day, Ledecky anchored the United States team of Allison Schmitt, Leah Smith, and Katie McLaughlin in the 4x200-meter freestyle relay.

[120][121][122] Friday June 18, 2021, the sixth day of competition, Ledecky won with a time of 8:16.61 in the prelims heats of the 800-meter freestyle and advanced to the final.

[123][124] The following day in the final, Ledecky won with a time of 8:14.62 and qualified to swim the 800 meter freestyle at the 2020 Summer Olympics for the United States.

The next day, Ledecky anchored for Team USA in the women's 4 × 200 freestyle relay, winning a silver medal alongside teammates Allison Schmitt, Paige Madden, and Katie McLaughlin behind China.

With four golds, Ledecky expanded her career World Championships medal haul to 22, passing Natalie Coughlin for most for a female swimmer.

[144] On the first day of competition, Ledecky won the 400-meter freestyle in a championship record 3:58.15, besting Canadian silver medalist Summer McIntosh by 1.24 seconds.

Ledecky's time of 3:58.73 topped New Zealand's Erika Fairweather (3:59.59) and Canada's Summer McIntosh (3:59.94) in the first women's 400-meter race that saw four swimmers break the 4-minute barrier.

[152] Ledecky joined Erin Gemmell, Bella Sims, and Alex Shackell to earn the silver medal in the 4 × 200 m freestyle relay.

[161] She won her fourth consecutive gold medal and eighth individual gold (an all-time record for women at the Olympics, a new all-time record for women at the Olympics, the previous one set by gymnast Věra Čáslavská had stood for 56 years) in the 800 metre freestyle and also competed in the 4x200m freestyle relay, joined by Claire Weinstein, Paige Madden, and Erin Gemmell.