The season also sees the debut of Matthew Waterhouse as Adric, Sarah Sutton as Nyssa, and Janet Fielding as Tegan Jovanka, the three of whom would remain regular companions into the Fifth Doctor's era, as well as the return of the Master, portrayed both by Geoffrey Beevers and Anthony Ainley.

New companions Adric (Matthew Waterhouse), Nyssa (Sarah Sutton), and Tegan Jovanka (Janet Fielding) make their introductions in Full Circle, The Keeper of Traken, and Logopolis, respectively.

Romana, played by Lalla Ward, departs from the series in Warriors' Gate, along with John Leeson who returns to voice the robot K9.

After the events of Traken, the Master was thereafter played by Anthony Ainley, who would continue in the part for the rest of the classic series' run.

Over the period of Christmas 1980, the season took a two-week transmission break between the broadcasts of State of Decay and Warriors' Gate.