Johnson started her women’s football career at the age of 16 in 2010 playing for Leicester City for two seasons, which resulted several call-ups to England's U19s.
After Johnson's time with the Foxes, the defender moved to Coventry City whilst attending Loughborough University for four seasons, winning the Southern Premier League in 2014.
In 2016, Palace's summer signing moved to Durham WFC, where the defender played for two-and-a-half years whilst studying for a masters during her time with the WSL side.
Johnson's leadership qualities saw her chosen to represent Team GB as a captain at the World University Games in Taipei in 2017.
After a season with London Bees during the last campaign, Johnson made the move to the Eagles in the summer of 2019.
Following the departure of Freya Holdaway at the end of the 2019/20 season, Johnson was named captain.