The special track is a reworking of the BBC show's long-standing alternative tune 'Julia's Theme', which traditionally airs at the end of episodes featuring intense emotion or drama.
'Peggy's Theme' has been created by Simon May, who composed the original EastEnders theme in 1984 and is also known for creating the theme tunes for several other shows, including Howards' Way and Eldorado.
The extent to which the new tune will differ from 'Julia's Theme' - recognisable for a slow piano build-up leading into the end credits - is currently unclear.
A BBC spokesperson today confirmed to DS that Peggy's final episode will feature the special theme. However, with details of the matriarch's final moments in Albert Square being kept closely under wraps, further information has not been disclosed.
Barbara Windsor, who plays Peggy, announced her decision to leave EastEnders last October. Her last episode is due to air next month.
Meanwhile, it has also been confirmed that 'Peggy's Theme' will be the lead track on compilation album The Simon May Collection, which is to be released on September 13.