At the 2012 Summer Olympics in London, Meilutytė won the gold medal in the women's 100 metre breaststroke with a time of 1:05.47.

In the final of the same event, Meilutytė won the silver medal and for the third time set a new national record of 58.79 seconds.

[19] On the third day of the Championships, Meilutytė competed in 100 metre breaststroke heats, where she placed first and set a new national record of 1:04.69.

[22] On the same day in the 100 metre breaststroke semi-finals Meilutytė broke the World record in 100 metre breaststroke, finishing with a time of 1:04.35 seconds and becoming the first record-holder of the championships[23] and the first Lithuanian athlete to break a swimming world record since Lithuania gained independence from the Soviet Union in 1990.

[24] During the 100 metre breaststroke final, she won the gold medal, by beating Yuliya Efimova (1:05.02) and Jessica Hardy (1:05.52) with a time of 1:04.42.

On the next and the last day of the championships, Meilutytė competed in 50 metre breaststroke final, where she won the silver medal with a time of 29.59.

[28] In her first event, 50 metre breaststroke heats, Meilutytė qualified to the semi-final with a time of 31.10 seconds and broke Championship record.

During 100 metre freestyle final, Meilutytė won silver medal, finishing behind Siobhan Bernadette Haughey (54.47) with a time of 54.94 seconds.

[31] During the 200 metre individual medley final, she won gold medal, by beating Emu Higuchi (2:15.15) and Ella Eastin (2:15.34) and broke Championship and Lithuanian swimming record.

Meilutyte also competed in 4×100 metre mixed medley with Danas Rapšys, Povilas Strazdas, Eva Gliožerytė.

On the overall women's scoring of the 2013 FINA Swimming World Cup, she placed fourteenth with total of 80 points.

[36] Meilutytė also competed in 50 metre freestyle heats, where she placed tenth with a time of 25.18 seconds and did not qualify to the final.

In 100 metre individual medley final, Meilutytė won her third gold medal at 2013 FINA Swimming World Cup, by beating Katinka Hosszú (58.75) and Alia Atkinson (59.12) with a time of 58.57 seconds.

During the 50 metre breaststroke final, she won the gold medal, by beating Julia Willers (31.78) and Anna Sztankovics (31.84) with a time of 30.14 seconds.

On the next day of the 2014 Summer Youth Olympics, Meilutytė competed in 100 metre breaststroke final, where she won the gold medal with a time of 1:05.39.

[45] On 24 August 2014, Meilutytė competed in the 50 metre breaststroke final, where she won the gold medal with a time of 29.89 seconds, thus making it the last gold medal she needed to reach first ever Aquatic Grand Slam, which requires to win gold medal in swimming events at Olympic Games, Youth Olympic Games, FINA World Senior (long-course and short-course) and Junior Championships, Swimming World Cup, European Youth and Senior Championships (long-course and short-course).

During the 50 metre breaststroke final, Meilutytė won gold medal, by beating Alia Atkinson (29.66) and Lillia King (30.13) with a time of 29.36 seconds.

In September 2015 Meilutytė suffered an injury to her elbow while riding a bike from her home at Plymouth to her training camp.

Meilutytė managed to finish in fourth place on the final round by twenty-one hundredths of a second (0.21) behind American Katie Meili, clocking at 30.20.

Russian Yuliya Yefimova placed second and Meili's teammate Lilly King broke another World Record with a time of 29.40.

On the next day of the 2018 European Aquatics Championships, Meilutytė competed in 100 metre breaststroke final, where she won the silver medal with a time of 1:06.26.

In early May 2019, Meilutytė was facing at least a one-year suspension for not being present for doping tests in April 2018, August 2018, and March 2019.

[2] Five days later, Swimming World officially called her career as permanently over, with no prospects of ever returning to competition, and dubbed her actions the "Fall of an Olympic Champion".

[58] Four days earlier, NBC Sports propagated the same sentiment, including that she was a "shock Olympic swimming champion".

[62] At the 2022 World Aquatics Championships she won the bronze medal in the women's 100 metre breaststroke, finishing behind Anna Elendt (1:05.98) and Benedetta Pilato (1:05.93) with a time of 1:06.02.

[64] For her first event at the 2022 European Aquatics Championships, held in August in Rome, Italy, Meilutytė won the bronze medal in the 100 metre breaststroke with a time of 1:06.50, which was 0.53 seconds slower than gold medalist Benedetta Pilato and 0.16 seconds behind silver medalist Lisa Angiolini of Italy.

[71] The following stop of the circuit, in Toronto, Canada beginning 28 October, Meilutytė started off with a seventh-place finish in the final of the 100 metre individual medley on day one with a time of 59.67 seconds.

[72] On the second day, she won the gold medal in the 100 metre breaststroke with a time of 1:02.95, which made her the only female to swim faster than 1:03.00 in the final.

[76] In the 100 metre individual medley on day one of the stop in the third and final location, Indianapolis, United States, Meilutytė placed seventh with a time of 59.58 seconds.

[80] At the 2022 World Short Course Championships, held in Melbourne, Australia, Meilutytė ranked first in the preliminaries of the 100 metre breaststroke on day two with a time of 1:03.81 and qualified for the evening semifinals.