The BBC One adaptation of Winston Graham's books stars Aidan Turner as Cornish captain Ross Poldark, and the actor confirmed that fans would see another run of the programme.
Speaking at a panel for the show at the BFI And Radio Times Television Festival, Turner said: "We start filming series four in September."
The third series will air in June and is based on books five and six from the 12-novel series, The Black Moon and The Four Swans.
Another period hit, The Durrells, also had news for fans at the London event.
The ITV series, which is set in Corfu, had its season two premiere at the festival followed by a discussion with the cast and crew.
At one point, writer Simon Nye said: "They got some exotic new - that's series three, some exotic new animals."
Event host Kirsty Lang asked: "You mentioned series three. It hasn't actually been announced. Is there going to be a series three?"
Nye confirmed that the script was written and star Keeley Hawes was due to fly out to Corfu in three weeks to begin production.
Series two of The Durrells will air on ITV later in April.