Catherine Johnson (born 14 October 1957) is a British playwright, producing works for stage and television. She is best known for her script for the musical Mamma Mia! and screenplay for the film of the same name, which became the highest grossing UK film of all time and the biggest selling UK DVD of all time in January 2009.

Johnson grew up in Wickwar near Wotton-under-Edge and attended Katherine Lady Berkeley's school in Wotton. She was expelled from school at 16, married at 18 and divorced by the age of 24. She moved to Bristol and finding herself unemployed and with one child to support and another on the way she spotted a notice in the local paper for the Bristol Old Vic/HTV West playwrighting competition. She wrote Rag Doll, using the pseudonym Maxwell Smart, a play about incest and child abuse, which won the competition and was staged by the Bristol Old Vic. Further plays for the Bush Theatre in London, Bristol Old Vic and Show of Strength followed along with work on television series including Casualty, Love Hurts and Byker Grove. Johnson lives in Bristol and also owns a house in Pimlico, London.

In 2007 Johnson instituted The Catherine Johnson Award for Best Play written by the five Pearson Playwrights' Scheme bursary winners from the previous year. Catherine won a bursary from the scheme in 1991. Catherine is a patron of the Electric Picture House in Wotton-under-Edge and Arts and Community in Thornbury.