Benjamin, 25, who first joined the cast of the long-running BBC soap in May 2006, said the decision to quit had been "very difficult" but the time was right to move on.
Scriptwriters are now expected to pen her departure scheduled for later in the year.
In a statement issued via the BBC, she said: "I have had an amazing time at EastEnders and this has been a very difficult decision but now seems the right time to move on and leave Chelsea behind, even though she's been such a fantastic character to play."
Some of Chelsea's most memorable story lines have included the discovery of a half-brother, tracking down her father and developing a cocaine habit.
A description on the BBC's EastEnders website says of Chelsea Fox: "Yes, she might seem vain, indulged, and argumentative, but that's just the shield she puts up to protect herself from the world.
She's not as tough as she makes out."
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