A spokesperson for Patsy, 41, said that the actress, who plays Bianca Butcher, was "really sad" to be leaving the long-running soap but felt it was the right time in her career to move on to other projects.
"Patsy is really sad to be leaving the show as she loves playing Bianca and working with executive producer Dominic Treadwell," said the rep. "But she knows it's the right decision at this time in her life."
EastEnders's exec producer Dominic added: "We are so sad that Patsy has decided to leave us but completely understand that it's the right time for her."
The character of Bianca will remain on screens until autumn, with Dominic promising viewers can expect "a lot more to come from her" until then.
He also assured viewers that Bianca will not be killed off. "The door will be left open for her return," he said. "We won't be getting rid of Bianca's puffa jacket just yet."
According to The Mirror, Patsy is planning to move her family to Los Angeles later this year in order to pursue a "once in a lifetime opportunity" although details have not been revealed.
A source told the newspaper: "She has lots of exciting offers lined up and feels the time is right to say goodbye."
Patsy joined EastEnders in 1993 and was a major character until quitting in 1999. She returned briefly three years later, before rejoining as a full cast member in 2008.
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