The actress will reprise her role of Kate Stewart, daughter of the legendary Brigadier Lethbridge-Stewart, played in the original series by Nicolas Courtney.
Courtney first appeared as the Brigadier in 1968 opposite Patrick Troughton’s Doctor. He became a series regular in the Jon Pertwee era and appeared opposite both the 5th and 7th Doctors.
He also appeared in Who spin-off The Sarah Jane Adventures alongside former companion Sarah Jane Smith (Elisabeth Sladen).
Last year’s introduction of Kate Stewart followed Courtney’s off screen death and the off-camera death of his character. Her arrival in the series serves as a link back to the show’s early years.
Redgrave is the latest casting announcement for the fiftieth anniversary special which is currently filming and will be shown in 3D in cinemas and on TV.
Earlier this month the BBC confirmed that former series stars David Tennant and Billie Piper will team up current Tardis crew Matt Smith and Jenna-Louise Coleman for the anniversary special.
The two Doctors and their companions will be joined by screen legend John Hurt and Gavin & Stacey star Joanna Page.