The creator and show-runner of the critically acclaimed drama has said that Peggy, who is played by Elizabeth Moss, will definitely appear despite leaving her job at Sterling Cooper Draper Pryce at the end of last season.
Moss had previously hinted that her character may return, but Weiner has now confirmed it in an interview with TVLine, saying: "I will spoil that one tiny piece of anticipation and tell people that Elisabeth will be showing up to work.
"I can't say how much [she will be on the show next year], in what capacity or what [her story] is going to be, but she has not left the show."
The writer and producer compared fan speculation over Moss's departure to that that ensued after Don and Betty divorced, adding: "Everyone was like, 'I guess January Jones is off the show', and I was like, 'Why would she be?' I never understood that."
Weiner also said that while the show has only officially been renewed for season six, a seventh run is all but a certainty, arguing: "We cannot rely on the official language of things. There will be a season seven.
"Jon Hamm is signed on for it, I'm signed on for it… I mean, if season six has one viewer... but I don't think [ratings] is what it's about. I think season seven has already been internationally sold... It's going to happen."
Mad Men is shown on AMC in the US, and Sky Atlantic in the UK.
Watch Digital Spy's interview with Mad Men star Jon Hamm below: