Hannah Margaret McNair "Maggie" Mac Neil[note 1] OLY (born 26 February 2000) is a Canadian former competitive swimmer.

"[7] She competed for Sir Frederick Banting Secondary School and the London Aquatic Club prior to her acceptance at the University of Michigan.

[9] Mac Neil concluded her time at the University of Michigan with two bronze medals at the 2022 NCAA Division I Women's Swimming and Diving Championships.

[10] On 25 March 2022, she announced that she would be transferring to finish her final year of NCAA eligibility at the University of California, Berkeley, where she would be beginning graduate studies in sports management.

[13] In her final appearance at the SEC championships, Mac Neil helped the Lady Tigers win a record fifth gold medal.

[14] She concluded her college career at the 2023 NCAA Division I Women's Swimming and Diving Championships, setting a record time in the 50 yard freestyle event and winning the gold medal.

[16] After various age group successes domestically, Mac Neil appeared in her first international competition in 2015, winning two butterfly finals at the Arena Pro Swim Series in Orlando.

Performing well at the 2015 Canadian trials, she was selected to make her major international debut at the 2015 FINA World Junior Swimming Championships in Singapore.

[18] Based on her trial results, she was assigned to compete at the 2016 Junior Pan Pacific Swimming Championships in Maui, where her best individual placement was fifth in the 100 m butterfly.

[20] She improved the following year, doing sufficiently well at the 2018 Canadian national trials to qualify for the 2018 Pan Pacific Swimming Championships, earning the FINA "A" standard in both the 100 m freestyle and 100 m butterfly, finishing the runner-up in the latter event behind reigning Olympic silver medallist Penny Oleksiak.

[19] Competing in Fiji, Mac Neil won her first major international medals, most notably her first championship title in the 100 m butterfly, where she set an event record of 58.38.

She first won a bronze medal as part of the 4×100 m freestyle relay team, alongside Penny Oleksiak, Taylor Ruck, Kayla Sanchez, and Rebecca Smith.

Mac Neil then competed in and won gold in the women's 100 metre butterfly,[22] beating four-time World and reigning Olympic champion Sarah Sjöström, in what was considered a major upset.

[23] She closed out the championships as part of the Canadian 4×100 m medley team, swimming the final with Kylie Masse, Sydney Pickrem and Oleksiak.

[24] Her plans for the 2020 international season were significantly disrupted by the onset of the COVID-19 pandemic, which ultimately delayed the Summer Olympics by a full year.

[26] The following day, Mac Neil competed in the final of the 100 m butterfly event, taking the gold medal by a margin of 0.05 seconds over China's Zhang Yufei, setting a new personal best and Americas record of 55.59.

[30] At the end of the year, Mac Neil was part of the Canadian delegation to the 2021 FINA World Swimming Championships (25 m) in Abu Dhabi, the top international event competed in a short course pool.

[34] Mac Neil swam the anchor leg for the Canadian team in the heats of the 4×100 m mixed freestyle relay, helping them qualify to the event final in second place.

[36] Named to her first Commonwealth Games team, Mac Neil began the first day of the championships by winning the bronze medal in the mixed 4×100 m freestyle relay, and qualifying to the event final of the 100 m butterfly with the second-fastest time in both the heats and semi-finals.

"[56] As with most of the Canadian team's top swimmers, Mac Neil opted not to attend the 2024 World Aquatics Championships in Doha, citing its proximity to the Summer Olympics.

[58] Mac Neil next attempted to defend her Olympic title in the 100 m butterfly, but fell short, finishing in fifth place, 0.23 seconds behind bronze medalist Zhang Yufei.