Marsha Thomason was born and raised in Manchester, England. Her love for acting began after watching the musical Bugsy Malone. Soon after, aged twelve, she joined Oldham Theatre Workshop, where she performed many diverse stage plays, including 'Our Day Out' by Willy Russell and 'Peace' by Aristophones. What began as a hobby soon helped her achieve her first professional acting job at the age of fourteen, when she starred in 'The 8:15 from Manchester' (BBC 1). Marsha took 'A' levels in English Language, Media Studies and Theatre Studies before studying for her BA in English at Manchester Metropolitan University. Whilst at university, Marsha won the role of Janice Lafferty in Prime Suspect 5: Errors of Judgment alongside Helen Mirren, and later the same year, she appeared in Brazen Hussies with Julie Walters and Robert Lindsay. Many parts followed, including Sally in the BBC's popular series, Pie in the Sky.

Aged twenty, Marsha moved to London's Notting Hill to take the role of Shazza Pearce in Playing the Field, in which she played a beer-swilling, drug-taking soccer player. This was a role close to her heart as a life-long Manchester City supporter. After the first series of Playing the Field, Marsha also starred as Nurse Jacqui Richards in Where the Heart Is. She appeared in both programmes simultaneously for three years. At this point, she was spotted by Red Productions and appeared in Love in the 21st Century, a series of six adult morality tales.

Marsha fulfilled a life-long dream of starring in London's West End when she made her professional stage debut in 'Breath Boom' at the Royal Court Theatre. The play was also the debut of Marsha's American accent, as her character was a fifteen-year-old prostitute from New York whose dream of acceptance was to belong to a girl gang.

Marsha's first foray into feature film was the Working Title production Long Time Dead, a British horror film also starring Lukas Haas and Alec Newman. Her career then took her to America where she has continued to work in film with roles as diverse as Victoria in Black Knight starring Martin Lawrence, and Brandy in Miramax's My Baby's Daddy. She returned to England for the independent feature, Pure, directed by Gillies MacKinnon. Considered her most ambitious role to date, Marsha played Vicki, a cockney heroin-addicted prostitute. Whilst still in England, Marsha returned to Red Productions for the first series of the critically acclaimed Burn It.

In 2002, Marsha was awarded Best Actress in Film at the BFM awards. She recently appeared in the Disney feature The Haunted Mansion in which she starred opposite Eddie Murphy.