The Walford student, played by actress Bunmi Mojekwu, will bow out on screen in the summer after a year as a regular cast member on the show.
Mercy is currently caught up in an immigration drama after the UK Border Agency threatened to deport her for outstaying her visa.
Since then, the character has accepted a proposal of marriage from best friend Fatboy Chubb (Ricky Norwood), who is determined to keep her in the country but also harbours real feelings for her.
Details of Mercy's departure are being kept under wraps, so it is currently unclear whether her exit will tie in with the current plotline or a different story altogether.
An EastEnders spokesperson confirmed to DS this afternoon that Mercy will leave screens in July.
They added: "Bunmi has done a great job of bringing the role of Mercy to life and we wish her every success in the future."
Mercy was first introduced as a cast member on internet spinoff EastEnders: E20 in January 2010. Initially, she was the only character who did not move over to the main show, but Mojekwu later landed an EastEnders deal and began making regular appearances from May.
As Leon Small (Sam Attwater) and Zsa Zsa Carter (Emer Kenny) have also left EastEnders, the news means that Fatboy will be the only E20 star to remain in the main programme.
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