It's the second time the 25-year-old, who plays Sam Mitchell, has been dumped.
She was first written out four years ago when fans saw her character leave to start a new life in Spain.
A BBC spokesman said: "Danniella Westbrook's contract has not been renewed.
"Her character Sam Mitchell will move to north London, leaving the door open for her to return in the future."
Westbrook, who originally joined the soap in 1990, added: "I will always love working on EastEnders, especially with the cast.
"Sam's departure to north London gives me the chance to explore more opportunities."
Speaking on London radio station Capital FM, she denied she had been sacked, saying she decided to leave because she is getting married and she wanted to spend time with her boyfriend.
"We're going to go on a few holidays and I've been offered two films and a play to do.
"I'll maybe go back to EastEnders in six months, so it's an amicable split."
Westbrook's latest exit from Albert Square follows newspaper speculation about her private life.
At the age of 21 the actress admitted spending £100,000 on cocaine over a two-year period.
Westbrook only returned to the soap last summer. Her character has most recently been involved in an on-off relationship with club owner Beppe di Marco, played by Michael Greco.