The pair - who play bipolar-suffering mother-daughter duo Stacey Branning and Jean Slater - will step down from their roles after almost six years, with Turner in particular expressing her desire to pursue other acting opportunities.
The door for a potential return will be firmly left open for Stacey, while Jean's future has yet to be determined.
Storyliners are currently working on dramatic departures for the two characters.
Speaking of her decision to leave, Turner said: "I've had the most fantastic time at EastEnders. Stacey has been such a brilliant role for me to play, as has being part of the feisty Slater family.
"I'm so lucky to have had such challenging storylines, from the affair with Max and being diagnosed with bipolar to the complete shock of being revealed as Archie's killer during the live 25th Anniversary episode."
She added: "I'll miss Stacey and everyone in Albert Square very much but the time has come to try something different."
"It's only right that someone as talented and versatile as Lacey should pursue new challenges and we wish her the very best of luck."
He continued: "In the meantime, viewers can look forward to a typically dramatic Slater family exit when she leaves and the door will be left open for Stacey Branning to return to Albert Square in the future."
Meanwhile, Wright (above left) said of her departure: "It's been an honour to play Jean especially as the public response to her has always been so supportive. It's been a real privilege to be able to heighten awareness of bipolar disorder.
"I've thoroughly enjoyed working with my onscreen Slater family, in particular working with Lacey and developing such a great rapport over the years."
Kirkwood added: "Gillian has brought real heart and pathos to the role of Jean Slater, a complex and fragile character who has really been taken into the public's affection."
Earlier this month, it was announced that head of the Slater clan, Charlie - Derek Martin - is to leave along with five others.
Turner first appeared in the Albert Square soap in November 2004 and has been a regular ever since, while her screen mother Wright made her brief debut the following month. She reappeared a year later for another short stint, before joining full-time from November 2006.