The actress signed up to play PC Beth Green on the ITV1 programme in January 2007. She had previously starred as Ruby Allen in EastEnders for 18 months, but she was written out of the BBC One soap after producers decided that there was nowhere for her character to develop.
Lytton has now told Bill producers that she wants to leave when her current contract expires in the autumn.
"I'm only in The Bill until October, then it's finished," Lytton told The People. "As yet, I don't know what I am going to do next."
A spokeswoman for the police drama added: "She has chosen not to renew her contract when it ends later this year. Louisa has decided to move on after two years to try new things."
Lytton was recently chosen to represent the UK at the Eurovision Dance Contest in September. She will be joined by Vincent Simone, who was her partner on the fourth series of Strictly Come Dancing in 2006.