He won the gold medal in the 400 metres hurdles at the 2024 World Athletics U20 Championships.

[2] In 2024, he was named the Gatorade athlete of the year for Arizona and signed a letter of intent to study at the University of Florida.

[3] In May 2024, Nilsson ran 34.83 seconds in the 300 metres hurdles to set a new national high school record at the AIA State High School Track & Field Championships in Mesa, Arizona.

That month, he competed in the US Olympic Trials in Eugene, Oregon where he ran 49.77 seconds, the fourth-fastest time by an American high schooler.

[6] In August 2024, he ran a 49.26 personal best to win the gold medal in the 400 metres hurdles at the 2024 World Athletics U20 Championships in Lima, Peru.