She began her defense of her title with a stunning new world record when she returned to Chicago in October 2019, taking over a minute off Paula Radcliffe's previous mark with a time of 2:14:04.
Kosgei had a string of podium finishes to her name before eventually taking first place in an AbbottWMM race with her Chicago victory.
She followed that up with a personal best 2:18:20 in London to become the youngest woman to win the event. 2019 also saw her win the prestigious Peachtree 10km road race in the United States before setting a new world best in the Great North Run half marathon in the UK of 1:04:28.
In 2020 she won the elite-only Virgin Money London Marathon in 2:18:58. Since transitioning to the marathon distance in 2015, Kosgei has finished first or second in all but one of her ten 26.2-mile races.