The Albert Square icon will make her final Walford appearance later this year following Barbara Windsor's decision to quit the role.
Plans for Peggy's exit plot have now been finalised and her swan song episodes are expected to be penned by the BBC soap's lead writer and series consultant Simon Ashdown.
Speaking to Walford Web, Treadwell-Collins confirmed: "We've storylined Barbara's exit and that's going to be epic and moving - Simon's already chomping at the bit to write those episodes."
Meanwhile, on the impact that Peggy's departure will have, he commented: "It's a huge loss, but the show - and the Mitchells - will keep going. We've actually got an amazing story for the Mitchells over the next year or so. And maybe even some joy for Ronnie! It's time to give the girl a break."
Windsor admitted last month that she will be "so sad" to leave Peggy behind.