Laviai Nielsen is a British athlete specializing in sprinting. She participated in the women’s 400 meters at the 2017 European Athletics Indoor Championships, where she secured a fourth-place finish in the final.

Born on March 13, 1996, in Leytonstone, East London, she has an identical twin sister, Lina Nielsen, who is also a competitive athlete in the same events. Initially, she focused on middle-distance running; however, in 2013, both she and her sister were encouraged to transition to the 400 meters at an event. Laviai Nielsen subsequently improved her personal best in the 400 meters by 2 seconds within two months and achieved an additional four-second reduction by the next season.

Laviai Nielsen experienced a significant breakthrough in 2015, securing a gold medal in the 400 meters at the European Junior Championships held in Sweden. She further distinguished herself by running the final leg for the victorious 4 x 400 meters relay team, alongside her sister Lina, who participated in the second leg. That year, Laviai Nielsen also achieved a personal best of 52.25 seconds, marking the fastest time for an under-20 athlete in 2015 and ranking as the third-fastest performance ever recorded by a British junior athlete.

In February 2017, she set a new personal record of 51.90 seconds during an indoor competition in Birmingham. Later that summer, she advanced to the final of the 400m at the European Indoor Championships in Belgrade, where she finished fourth, narrowly missing a bronze medal by just 0.27 seconds. On the final day of the championships, she anchored the 4 x 400-meter relay team, earning a silver medal behind a formidable Polish team. Laviai Nielsen solidified her status as a double British champion by successfully defending her title in the 400 meters at the 2020 British Athletics Championships, clocking a time of 51.72 seconds.

Laviai Nielsen photos