The women's 100-metre butterfly event at the 2024 Summer Olympics was held from 27 to 28 July 2024 at Paris La Défense Arena, which was converted to a swimming pool for the swimming events.

Going into the competition, Gretchen Walsh of the US was the favourite, having set the event's world record at the Olympic Trials. Also among the favourites were China's Zhang Yufei and US' Torri Huske, while Canada's Maggie Mac Neil was the defending champion. In the semifinals, Walsh set a new Olympic record, but in the finals, Huske won by 0.04 seconds after coming back from over half a second behind over the last 35 metres. Walsh finished second, and Zhang finished third. Swimming World called Huske's win a "stunning victory", and it was the first time the US had won gold and silver in the event since 1984.

Two national records were set during the event: Barbora Seemanová broke the Czech Republic's record in the heats, and Roos Vanotterdijk broke Belgium's in the semifinals.

Background Canada's Maggie Mac Neil was the defending champion going into the event, and six of the finalists (including Mac Neil) from the previous Olympics were returning. Gretchen Walsh set a world record in the event at the 2024 US Olympic Trials, where Torri Huske had swum 0.21 seconds slower to claim the second qualification spot for the US. Huske also won gold at the 2022 World Championships, while China's Zhang Yufei—who also qualified for this event—won gold at the 2023 World Championships. Both SwimSwam and Swimming World predicted that Gretchen Walsh was most likely to win the race.

The event was held at Paris La Défense Arena, which was converted to a swimming pool for the swimming events.

Qualification Each National Olympic Committee (NOC) was permitted to enter a maximum of two qualified athletes in each individual event, but only if both of them had attained the Olympic Qualifying Time (OQT). For this event, the OQT was 57.92 seconds. World Aquatics then considered athletes qualifying through universality; NOCs were given one event entry for each gender, which could be used by any athlete regardless of qualification time, providing the spaces had not already been taken by athletes from that nation who had achieved the OQT. Finally, the rest of the spaces were filled by athletes who had met the Olympic Consideration Time (OCT), which was 58.21 for this event. In total, 40 athletes qualified through achieving the OQT, 35 athletes qualified through universality places and two athletes qualified through achieving the OCT.

+ Top 10 fastest qualification times Swimmer Country Time Competition Gretchen Walsh 55:18 2024 United States Olympic Trials Torri Huske 55:52 2024 United States Olympic Trials Zhang Yufei 55:86 2022 Asian Games Angelina Köhler 56:11 2024 World Aquatics Championships Maggie Mac Neil 56:45 2023 World Aquatics Championships Emma McKeon 56:58 2024 Australian Championships Yu Yiting 56:82 2024 Chinese Championships Mizuki Hirai 56:91 2024 Japanese Olympic Trials Louise Hansson 56:94 2024 World Aquatics Championships Lana Pudar 56:95 2023 European Junior Championships

Heats Four heats (preliminary rounds) took place on 27 July 2024, starting at 11:00. The swimmers with the best 16 times in the heats advanced to the semifinals. Zhang qualified fastest, swimming 56.50 seconds, while Barbora Seemanová lowered her national record for the Czech Republic by swimming 57.50—0.25 faster than her previous national record from the year prior.

+ Results Rank Heat Lane Swimmer Nation Time Notes 1 2 4 Zhang Yufei 56.50 2 4 3 Mizuki Hirai 56.71 3 3 4 Torri Huske 56.72 4 4 4 Gretchen Walsh 56.75 5 2 5 Emma McKeon 56.79 6 4 5 Angelina Köhler 56.90 7 3 5 Maggie Mac Neil 57.00 8 3 6 Alexandria Perkins 57.46 9 4 1 Barbora Seemanová 57.50 , NR 10 2 6 Marie Wattel 57.54 4 7 Roos Vanotterdijk 57.54 12 3 3 Louise Hansson 57.57 13 4 2 Erin Gallagher 57.80 14 4 6 Rikako Ikee 57.82 15 3 2 Tessa Giele 57.89 16 3 8 Keanna Macinnes 57.90 17 2 3 Lana Pudar 57.97 18 2 2 Hazel Ouwehand 58.03 19 3 7 Anna Ntountounaki 58.14 20 1 4 Helena Rosendahl Bach 58.45 21 3 1 Costanza Cocconcelli 58.66 22 2 8 Ellen Walshe 58.70 23 2 7 Georgia Damasioti 58.72 24 4 8 Rebecca Smith 58.85 25 1 5 Laura Cabanes 59.40 26 1 6 Varsenik Manucharyan NR 27 1 2 Oumy Diop 28 1 1 Ana Nizharadze 29 1 3 Luana Alonso 30 1 7 María Schutzmeier 31 1 8 Hayley Hoy 2 1 Viola Scotto Di Carlo

Semifinals Two semifinals took place on 27 July, starting at 20:30. The swimmers with the best eight times in the semifinals advanced to the final. Walsh qualified with an Olympic Record of 55.38 seconds, which broke Sarah Sjöström's record from 2016 by 0.10. Huske qualified in second, and Zhang in third. Roos Vanotterdijk broke the Belgian national record by swimming 57.25 seconds. This was 0.22 seconds faster than her previous national record set the month prior but was not enough to qualify.

+ Results Rank Heat Lane Swimmer Nation Time Notes 1 1 5 Gretchen Walsh 55.38 , OR 2 2 5 Torri Huske 56.00 3 2 4 Zhang Yufei 56.15 4 1 3 Angelina Köhler 56.55 2 6 Maggie Mac Neil 56.55 6 2 3 Emma McKeon 56.74 7 1 4 Mizuki Hirai 56.80 8 1 7 Louise Hansson 56.93 9 1 2 Marie Wattel 57.24 10 2 7 Roos Vanotterdijk 57.25 NR 11 2 2 Barbora Seemanová 57.64 12 1 1 Rikako Ikee 57.79 13 1 6 Alexandria Perkins 57.84 14 2 1 Erin Gallagher 57.90 15 2 8 Tessa Giele 57.91 16 1 8 Keanna Macinnes 58.11

Final The final took place at 20:40 on 28 July. Torri Huske started with the fastest reaction time of 0.63 seconds, but by 15 metres Gretchen Walsh had taken first place with a faster dive and underwater. By 25 metres, Zhang Yufei had taken the lead, but by 45 metres Walsh was back in front. At 65 metres (after the second turn and underwater) Walsh was over half a second ahead, having swum a 8.10 50–65 metre split, which was 0.5 seconds faster than anyone else in the race. Over the last 35 metres, Huske came from 0.69 behind to win by 0.04 seconds, pushing Walsh to second and Zhang to third. Matt Nelson, a journalist reporting on olympics.com, called the win a "stunning victory", while David Rieder of Swimming World said "It was a result three years in the making." It was the first time the US had won gold and silver in the event since 1984, and it was Walsh's first Olympic medal.

+ Results Rank Lane Swimmer Nation Time Notes 5 Torri Huske 55.59 4 Gretchen Walsh 55.63 3 Zhang Yufei 56.21 4 6 Angelina Köhler 56.42 5 2 Maggie Mac Neil 56.44 6 7 Emma McKeon 56.93 7 1 Mizuki Hirai 57.19 8 8 Louise Hansson 57.34

+ Statistics Name 15 metre split (s) 50 metre split (s) 50–65 metre split (s) Time (s) Stroke rate (strokes/min) Torri Huske 6.01 25.61 8.58 55.59 57.7 Gretchen Walsh 5.83 25.40 8.10 55.63 55.1 Zhang Yufei 5.95 25.42 8.65 56.21 61.9 Angelina Köhler 6.22 26.35 8.84 56.42 56.5 Maggie Mac Neil 6.27 25.94 8.43 56.44 61.0 Emma McKeon 6.17 26.40 8.69 56.93 54.3 Mizuki Hirai 6.45 26.66 8.51 57.19 59.8 Louise Hansson 6.18 26.61 8.61 57.34 56.4

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