As of 2024, Sjöström has won a total of 23 individual medals at long course World Championships, more than any other swimmer in history.

She is the only female swimmer to win five individual medals at a single FINA World Aquatics Championships, a feat she accomplished in 2019.

In 2021, Sjöström achieved a career total of over 1000 most valuable player points in the International Swimming League, becoming the first swimmer in history to do so.

In 2022, she became the first swimmer representing a country in Europe to win 10 individual World Championships gold medals.

On 22 March 2008, at the age of 14, Sjöström won the gold medal in the 100 metre butterfly at the 2008 European Aquatics Championships in Eindhoven, Netherlands, with a time of 58.44 seconds.

Sjöström earned a spot on the Swedish Swim Team for the 2008 Summer Olympics in Beijing, China, where she finished 27th in the preliminary heats of the 100 metre butterfly with a time of 59.08 and 29th in the preliminary heats of the 100 metre backstroke with a time of 1:02.38, failing to advance to the semi-finals in both races.

[18] In December 2011, she broke the Swedish record when she won the 100 metre freestyle at the Open Dutch Championships in Eindhoven.

[35] On 5 July 2014, Sjöström broke the world record in the long course 50 metre butterfly, set at 25.07 by fellow Swedish swimmer Therese Alshammar in 2009, with a time of 24.43 seconds.

[40] Approximately 30 minutes later, she won the gold medal in the 50 metre butterfly with a Championships record time of 24.58 seconds.

[59][60] On the third day, she shared the podium with two Dutch swimmers in the 100 metre freestyle, winning the gold medal with a time of 52.82 seconds.

[62] On 7 August 2016, Sjöström won the gold medal in the 100 metre butterfly at the 2016 Olympic Games in Rio de Janeiro, Brazil, setting a world record with a time of 55.48 seconds.

[97] Approximately 31 minutes later, she won her third and final gold medal of the night, splitting a 24.27 for the butterfly portion of the 4×50 metre medley relay to help place first in 1:44.43.

[98] In August, at the 2018 European Aquatics Championships in Glasgow, Scotland, Sjöström won the gold medal in the 100 metre butterfly on day two of competition with a time of 56.13 seconds.

The team won the overall title in the season finale in Las Vegas, United States, in December.

In the 2020 International Swimming League season Sjöström placed 5th overall in points in 2020, due in part to a back injury that made her sit out of a full match.

[115] And while neither were official world records, Sjöström also featured on Energy Standard's women's and mixed 4×100 freestyle relays that were both the fastest of all time.

[115] Due to a broken elbow Sjöström accidentally obtained by falling on ice in February 2020, she did not compete at the 2020 European Aquatics Championships.

[116][117] She returned to training in the pool in March and to competitive swimming in early June ahead of the 2020 Summer Olympics.

[117][118] In the 50 metre freestyle at the 2020 Olympic Games in Tokyo, Japan, and held in 2021 due to the COVID-19 pandemic, Sjöström won the silver medal.

[133] Sjöström won the silver medal in the final of the 100 metre freestyle later in the day with a time of 51.31, finishing less than four-tenths of a second behind gold medalist Siobhán Haughey of Hong Kong.

[136] The fifth morning, Sjöström advanced to the semifinals of the 50 metre freestyle ranking first by over three-tenths of a second with a 23.31 in the prelims heats.

[139] In her first final of the evening, Sjöström helped set a new Swedish record of 1:34.54 and win the silver medal in the 4×50 metre freestyle relay with a lead-off split of 23.33 seconds.

[141][142] In her final event of the championships, Sjöström split a 54.65 for the butterfly leg of the 4×100 metre medley relay, helping win the gold medal in a new European record time of 3:46.20.

[145] In January 2022, Sjöström was announced as one of the team Sweden members pre-nominated for the 2022 World Aquatics Championships in Budapest, Hungary.

[151] On the final day of competition, she started off with a gold medal in the 50 metre freestyle with a time of 23.98 seconds.

[153] Sjöström was one of twelve Swedish female swimmers named to the official roster for the 2022 European Aquatics Championships, held in August in Rome, Italy.

[160] In the morning session on day five, Sjöström started off ranking first in the prelims heats of the 50 metre freestyle with a 24.50, qualifying for the semifinals.

[163] With a 24.27 in the semifinals of the 50 metre freestyle, she qualified for the final ranking first, 0.09 seconds ahead of Katarzyna Wasick of Poland.

Despite being the World Record holder, Sjostrom had never won a gold medal in this distance at the global level.

In January 2022, Sjöström announced her engagement to her boyfriend of ten years, Swedish fencer Johan de Jong Skierus.