[8] At the 2024 Paris Olympics, he placed third in the 100-metre freestyle, earning the bronze medal, finishing just 0.01 seconds behind Australia's Kyle Chalmers.

[9] Popovici was born in Bucharest, Romania, and he started swimming at Lia Manoliu pool at the age of 4, at a doctor's recommendation to correct early stage scoliosis.

[10] At the age of 9 he began to train at Aqua Team Bucharest, under coach Adrian Rădulescu, a former swimmer with a PhD in athletic performance specialized in swimming.

[23] At the 2020 Summer Olympics in Tokyo, which were postponed to 2021 due to the COVID-19 pandemic, Popovici competed in the 50-metre, 100-metre, and 200-metre freestyle individual events, following his good performances at the European Championships.

On 6 November, Popovici won the gold medal in the Men's 200-metre freestyle event, with a time of 1:42.12, breaking his own national record from the World Cup.

[32][33] In his first of two events at the 2021 World Short Course Championships, the 400-metre freestyle on 16 December, Popovici placed thirty-second with a time of 3:46.08 and did not qualify for the evening final.

[37][3] This performance made Popovici the second-youngest swimmer to win the Men's 200-metre freestyle event at the world championships (following Tim Shaw), at only 17 years and 278 days old.

[39] On the next day, in the final, he managed to win his second gold medal, touching at 47.58 for a come-from-behind victory, just .06 ahead of France's Maxime Grousset.

[44] On 5 July, Popovici led off the Romanian Men's 4×100 freestyle relay in 47.54, as the quartet composed of himself, Vlad Stancu, Ștefan Cozma and Patrick Dinu won gold in front of a home crowd, with a time of 3:18.93.

[45][46] One day later, on 6 July, Popovici was part of the Romanian relay that won the silver medal in the Mixed 4x100-metre freestyle, along with Patrick Dinu, Bianca Costea, and Rebecca Diaconescu.

[51] On 13 August 2022, Popovici one-upped himself in the final, touching at 46.86 to not only win gold, but break César Cielo's 13-year-old world record in the event, by 0.05 seconds.

[56] On 14 August, he once again proved he was in top form in the 200-metre freestyle event, moving through the prelims and the semifinals easily, and dropping the hammer in the final the following day, clocking a new world junior record of 1:42.97, to win his second gold medal.

[59] Following the conclusion of the competition, LEN, the official governing body of European Aquatics, announced that David Popovici was named the male swimmer of the meet, as his performances earned him the highest number of FINA points during the championships.

[68][69] In his final event, Popovici swam in the 100-metre freestyle, winning his third gold medal, with a time of 47.13, 2.24 seconds ahead of silver medalist Jere Hribar.

He then showed no signs of faltering at the 150-metre mark with a 26.60 to remain under his best pace, but disaster struck on the last fifty meters, coming home in a sluggish 28.12, which saw him passed by Matt Richards, Tom Dean, and Hwang Sun-woo.

On 5 December, he swum in the Men's 4x50-metre Freestyle relay final, alongside Alexandru Stoica, Mihai Gergely and Patrick Dinu.

[94] In May 2023, Popovici donated one of the gold medals he won at the 2022 World Championships to charity, having it melted into little golden ribbons that were gifted as a sign of hope for children diagnosed with cancer.

[95] He also became an ambassador for the organization Hope and Homes Romania in April, which helps children get out of orphanages by finding them families to live with.