The actress, who is reportedly moving to Los Angeles in a bid to build a career in Hollywood, will leave the BBC1 show this year.
Show bosses have said they will not kill off her character but have not decided on the storyline that will see her leave Walford.
EastEnders executive producer Dominic Treadwell-Collins said: "We are so sad that Patsy has decided to leave us, but completely understand that it's the right time for her.
"Bianca won't be leaving Albert Square until the Autumn, so there's still a lot more to come from her on screen this year - and the door will be left wide open for her return. We won't be getting rid of Bianca's puffa jacket just yet."
A spokesman for the star said: "Patsy is really sad to be leaving the show as she loves playing Bianca and working with Dominic, but she knows it's the right decision at this time in her life."