The 2019 World Championships in Doha will culminate in a 4x400m mixed relay, the International Association of Athletics Federations has announced.
The event will make its global debut before its Olympic bow at Tokyo 2020.
The IAAF also announced the men's and women's marathons will begin at midnight, and morning sessions will be scrapped in favour of split evening sessions.
"We have some great World Championship firsts," said IAAF president Lord Coe.
"We are looking forward to seeing how these firsts and the engagement format will come together next year to deliver a World Championships that will look and feel different."
The International Olympic Committee (IOC) announced in June that mixed-gender events in athletics, swimming, table tennis and triathlon would be added to the Olympic programme for the Tokyo Games, including a 4x400m mixed relay in athletics.
At the time, the IAAF said it welcomed the introduction of mixed relays, but that it could be difficult to implement.
The 4x400m mixed relay title was won by the Bahamas at the IAAF World Relays in 2017.
In a statement announcing the competition schedule for the Doha event - to take place in the Qatari capital from 28 September to 6 October 2019 - organisers said they wanted to inspire and engage "new fans, new athletes and new audiences".
"It is our ambition to organise an innovative, creative and exciting event," said IAAF vice-president Dahlan Al Hamad.
Doha 2019 will "embrace" the latest trend of night running events by holding its men's and women's marathons at midnight, with the 20km and 50km race walks set to take place at 11:30pm.
The final events in both the decathlon and heptathlon will also take place after midnight.
Organisers also announced morning sessions would be removed from the timetable, with one-hour intervals being incorporated into evening sessions to combine fan entertainment with the sporting action.