Tegan first appears in the Fourth Doctor's last serial, Logopolis. Enroute to Heathrow Airport to start her new job as a stewardess with Air Australia, her aunt Vanessa's vehicle (in which she is riding) suffers a flat tire. Tegan enters a roadside police box to seek help, not knowing that it is actually the Doctor's disguised TARDIS. She is present when the Fourth Doctor falls from the Pharos Project radio telescope and regenerates into his fifth incarnation, and continues to journey with the Doctor and his other companions. She travels with the Doctor initially because her aunt was killed by the Master, although she still wants to get to Heathrow Airport to start her new job, as soon as the Doctor can get her there.
Tegan is stubborn, loud, and direct, with a no-nonsense manner and not afraid to speak her mind (in Earthshock she describes herself as "just a mouth on legs"). Her time in the TARDIS coincides with that of Adric, Nyssa, Turlough and Kamelion. While she often bickers with them (particularly with Adric) as well as with the Doctor, her strength of character keeps them together and her loyalty and affection to her fellow crewmates is unquestionable. She is close to Nyssa, and is especially saddened at her leaving. She is initially very suspicious of Turlough, frequently referring to him as a "brat" at first, though they gradually become friends. The Doctor notes that she is a good coordinator, and often encourages her with the words, "Brave heart, Tegan." She is apparently able to speak at least one Indigenous Australian language fluently, and shows an ability to use firearms.
Despite her strong front, however, her adventures with the Doctor, both thrilling and terrifying, eventually take a psychological toll. She is deeply upset by the death of Adric in Earthshock. After being left behind in Heathrow due to a misunderstanding at the end of Time-Flight she returns to the TARDIS in the next adventure Arc of Infinity, which is set about a year later in earth time. During that period Tegan had worked as a stewardess, but has been subsequently fired. Soon after she is once again possessed by the alien intelligence known as the Mara. Eventually, the carnage surrounding the events of Resurrection of the Daleks prove too much and she bids an emotional good-bye to both the Doctor and Turlough in 1984 London.
Tegan Jovanka is one of the few companions of the classic series to be seen to have an extended family. In addition to her Australian aunt Vanessa (Dolore Whiteman), her English maternal grandfather Andrew Verney (Frederick Hall) was seen to live in the village of Little Hodcombe in The Awakening, her English cousin Colin Frazer (Alastair Cumming) was terrorised by Omega whilst back-packing in Amsterdam during Arc of Infinity.
An illusory image of Tegan is seen during the Fifth Doctor's regeneration into the Sixth in The Caves of Androzani (1984).
Tegan is mentioned in the new series in the 2007 Children in Need special episode "Time Crash" by the Tenth Doctor when he is asking his fifth incarnation where he is in his own relative timeline.