Harrison held the world record in the women's 100 metres hurdles with a time of 12.20 seconds, set on July 22, 2016 at the London Müller Anniversary Games, breaking the previous world record of 12.21 seconds achieved nearly 28 years earlier by Bulgarian athlete Yordanka Donkova.

[5][6] Harrison transferred from Clemson to the University of Kentucky after the 2013 season, together with sprinter Dezerea Bryant and coach Tim Hall.

[5][9] In November 2015, Harrison was named as a 2016 recipient of the NCAA's Today's Top 10 Award, presented annually to 10 individuals who completed their athletic eligibility in the previous school year "for successes on the field, in the classroom and in the community.

[11] At the 2015 United States championships, which doubled as trials for the World Championships in Beijing, Harrison decided to concentrate on the 100 m hurdles only; she set a personal all-conditions best of 12.46w in the heats and ran a wind-legal 12.56 in the final, placing a close second to 2008 Olympic Champion Dawn Harper-Nelson and qualifying for the American team.

[12] Harrison opened her 2016 indoor season winning the 60 metres hurdles in Lexington, Kentucky, Karlsruhe, Germany and Glasgow in 7.92.

However, in the final she hit the first hurdle heavily and never recovered, ending in eighth while Nia Ali (the least favoured American) took the title.

[15][16] She began the outdoor season in April with the fastest opener recorded by a hurdler, 12.36 seconds, to go up to ninth on the all-time lists.