She has written several young adult novels and co-wrote the screenplay for the 2004 drama film Bullet Boy (directed by and co-written with Saul Dibb).

Johnson grew up in North London and attended Tetherdown Primary School.

She has since written and published 20 novels, including two for children about pioneering Arctic explorer Matthew Henson.

[6] Johnson won the 2019 Little Rebels Award for Radical Children's Fiction for her 2018 book Freedom.

[7][8] Johnson has been a Royal Literary Fund Fellow at the London Institute, a Writer in Residence at Holloway Prison and a Reader in Residence at the Royal Festival Hall's Imagine Children's Literature Festival.