Sharon attended Raines Foundation School in Bethnal Green, 1987–91.
She portrayed the role of Crystal Gordon in the first four series of ITV prison drama series Bad Girls. After leaving the programme at the end of its fourth series she guest-starred in Holby City, Waking the Dead, Babyfather and daytime soap opera Doctors. From February to September 2009 she appeared on the BBC soap opera EastEnders as Trina Johnson, estranged wife of Lucas Johnson. The character was killed off during a row with Lucas, who pushed her, impaling her throat on a rake. Brewster appeared in the 2009 Doctor Who special "The Waters of Mars" as Maggie Cain. Sharon also appeared on the medical TV series "Body Story" in 1998. In the episode, Sharon played a club singer and influenza patient named Holly Jones. The episode documented the radical transformations her character's body went through in order to stop the influenza virus. In 2011, she appeared in all four episodes of TV drama Top Boy. Brewster originated the role of "C" in the play Crave by Sarah Kane. She then played the role of Catherine Hunter who is Alex Hunter's mum in a football video game FIFA 17. Brewster repraised the role of Catherine Hunter in FIFA 18's Journey Season 2