In April 2018, he won his first major senior medal, with bronze for the 1500m at the Gold Coast Commonwealth Games, where he also finished fourth in the 800m. In June, he set a Scottish record for the 1000m with a time of 2:16.27 at the Diamond League meeting in Stockholm, breaking the previous record which had stood since 1984. Wightman took bronze in the 1500m at the Berlin European Athletics Championships in August. That year he became the first Briton to run below 1:45 in the 800m and 3:35 in the 1500m since Peter Elliott in 1991.
Wightman won the gold medal in the 1500m event at the World Championships in Eugene, Oregon in July with a personal best and world-leading time of 3:29.23, beating reigning Olympic champion and European record holder Jakob Ingebrigtsen (3:29.47). It was the first British world 1500m title since Steve Cram in 1983, the first Scottish world title on the track since Liz McColgan's 10,000m gold in 1991, and ended a streak of seven consecutive golds in the event from Kenya-born runners. The mark moved him to third on the UK all-time list. His father, Geoff Wightman, former marathoner and long-time media commentator, called the race as in-stadium commentator.
Wightman continued his good form in August by taking a bronze in his specialist event at the Commonwealth Games Birmingham 2022, and a silver for the 800m at the European Championships held in Munich.
In September, he broke the 1:44-barrier in the 800m for the first time, improving Tom McKean’s 33-year-old Scottish record of 1:43.88 in his fifth overall Diamond League victory with a time of 1:43.65 in Brussels. He capped his breakthrough season on the road a few days later, winning for the third time the Fifth Avenue Mile in New York (he also won in 2018 and 2021).
Going into the 2023 season, Wightman had aimed to defend his 1500 m title at the World Championships in Budapest. However, in January, after sustaining a foot injury, he spent 5 weeks in a boot and cross-trained. Wightman was able to run by the spring, aiming to be ready for Budapest. He was able to skip qualification given his status as the reigning world champion. However, after numerous achilles, shin, and hamstring issues, he withdrew from the World Championships. In his absence, his childhood schoolmate and club colleague, Josh Kerr, succeeded him as world champion in the 1500 metres.
In 2024, after missing the British Championships due to a calf injury, Wightman was selected to represent Great Britain in the 800 metres at the Paris Olympics. He pulled out just days before he was scheduled to race because of a hamstring injury. In autumn, Wightman made the decision to switch his training base from Teddington to Manchester so he could be closer to his physiotherapist.
2025–present
In March 2025, Wightman announced he would no longer be coached by his father Geoff. He is now coached by John Hartigan. In September 2025, Wightman won a silver medal in the 1500 metres at the 2025 World Athletic Championships.
