The teams of France, Great Britain, Belgium, Jamaica, Nigeria, and Switzerland all broke their national records in round 1.

[citation needed] (Justin Robinson, Rosey Effiong, Matthew Boling, Alexis Holmes) (Karol Zalewski, Natalia Kaczamarek, Justyna Święty-Ersetic, Kajetan Duszyński) (Christopher O'Donnell, Rhasidat Adeleke, Thomas Barr, Sharlene Mawdsley) (Zablon Ekwam, Mary Moraa, Kelvin Tauta [de], Mercy Chebet) (Musa Isah, Aminat Yusuf Jamal, Salwa Eid Naser, Abbas Abubakar Abbas) (Karol Zalewski, Natalia Kaczamarek, Justyna Święty-Ersetic, Kajetan Duszyński) (Justin Robinson, Rosey Effiong, Matthew Boling, Alexis Holmes) (Bendere Oboya, Anneliese Rubie-Renshaw, Tyler Gunn [fr], Alex Beck) (Jhon Perlaza, Lina Licona, Nicolás Salinas [de], Evelis Aguilar) For the mixed 4 × 400 metres relay event, fourteen teams qualified through the 2024 World Athletics Relays.

[8] In the first heat, USA started off with 44.1 s Vernon Norwood who ran an evenly paced 44.47 s leg, which looked like a fast close to handoff a step ahead of France's Muhammad Abdallah Kounta.

Shamier Little had lined up at the wrong end of the passing zone, the markings on the Paris track being faint "chevrons" instead of the large triangles more common in the USA.

In the rain, the race started off similar to the first heat, with Norwood looking behind the field but closing strong, but Doom handed off to Helena Ponette a step ahead.

Little reached the break line first, but she was followed closely by Ponette and world indoor silver medalist Lieke Klaver.

Deadmon continued Little's lead, with Belgium's Jonathan Sacoor gaining second place as the Dutch had a poor handoff from Klaver to Isaya Klein Ikkink.

Brown's final lap was 49.23 s, Anning 48.86 s, but they were no match to Bol's 48.00 s.[11] The Netherlands' winning time was 3:07.43 min, just one fiftieth short of the world record set the day before.