[5] In March 2013, Warholm won eight gold medals in the Norwegian Youth Indoors Championships.

[2] In June at the 2013 Bislett Games, he competed in the 200 metres, finishing seventh in his heat with a time of 22.25 s. Usain Bolt won a different heat at the same meet with a time of 19.79 s.[6] At the 2013 World Youth Championships in July, he won gold in the boys' octathlon with 6451 points, a personal best.

[11] In July 2016, while participating in the semi-final of the 400 m hurdles at the 2016 European Championships, he broke the Norwegian national record with a time of 48.84 s.[12] He then finished sixth in the final, with a time of 49.82 s. In August, he made it to the semi-finals in the 400 m hurdles at the 2016 Rio Olympics.

[17] In June at the Bislett Games in Oslo, he broke the European men's 400 m hurdles record with a time of 47.33 s.[18] At the Müller Anniversary Games in July, Warholm improved on his 400 m hurdles time, taking it to 47.12 s.[19] At the Weltklasse Zürich in August, Warholm set a new European record in the event, with a time of 46.92 s, making him the third person to run under 47 seconds for the distance.

He was chased to the finish line by Rai Benjamin, who became the fourth person to break 47 seconds, with a time of 46.98 s.[20] At the 2019 World Athletics Championships in Doha, Qatar, he won the 400 m hurdles in a time of 47.42 seconds, retaining his championship title from 2017.

He also ran 400 m indoors with a time of 45.97 s.[22] On 23 August in Stockholm, Warholm ran a personal best of 46.87 s, narrowly missing Kevin Young's world record of 46.78 s. With this performance, Warholm became the first person to break 47 seconds twice.

[25][29] On 4 September 2024, ahead of the Zurich Diamond League, Warholm competed in an exhibition 100m event against pole vault world record holder Mondo Duplantis.