This is a list of characters from the British science fiction television programme Torchwood, created by Russell T Davies. This list includes main characters, recurring characters and important guest characters. The main characters typically function as a team, defending the planet from alien and nefarious human threats. The series operated with a "monster of the week" format for its first two series before adopting a serial-based format for its third and fourth series, which feature an extended recurring cast of supporting characters.

Jack Harkness, played by Scottish-American actor John Barrowman, is the leader of Torchwood Three. A former Time Agent born in the 51st century, Jack had two years of his memories wiped by the Time Agency and subsequently became a con man operating in the 20th century, where he stole the name of "Captain Jack Harkness"; his real name is unknown. After meeting the Ninth Doctor in Doctor Who, Jack reformed and changed his ways, and after a stint as the Doctor's time travelling companion found his way to Torchwood in the 19th century. Cursed with immortality following his previous adventure with the Doctor, Jack served Torchwood on-and-off for centuries, eventually becoming its leader at the start of the 21st century, and handpicking a new team for himself thereafter. As a result of his immortality, Jack has lived a long life, in which he has seen the loss of his brother Gray, his grandson Stephen, and numerous lovers, both male and female. Including Gwen Cooper and Ianto Jones.

Gwen Cooper, played by Welsh actress Eve Myles, was recruited into Torchwood Three in the series premiere "Everything Changes". A policewoman, partnered with PC Andy Davidson, Gwen by the second series becomes elevated to the team's second-in-command in her own mind, after taking control as leader during Jack's absence. Despite their relationship being tested by Gwen's dishonesty, feelings for Jack Harkness and a tempestuous affair with Owen Harper, Gwen and her live-in boyfriend Rhys eventually get married. Jack still has feelings towards Gwen, when he comes back he finds out that Gwen is married and gets disappointed. Gwen is one of two surviving agents following the destruction of the Cardiff branch of the Torchwood Institute, and goes into hiding following the birth of daughter Anwen. During Miracle Day she is conflicted between her Torchwood duties and her responsibility to her baby daughter and severely ill father.

Her family has lived in Wales for generations, and it is suggested by the Doctor (David Tennant) and Rose Tyler (Billie Piper) that Gwen is related to the Gwyneth (also portrayed by Eve Myles) whom they met in Cardiff in 1869 in "The Unquiet Dead", due to spatial genetic multiplicity.

Doctor Owen Harper, played by American-born English actor Burn Gorman, is Torchwood Three's medical officer. After he loses his fiancée to an alien parasite, Owen's genius and determination are recognized by Captain Jack and he is recruited into the institute. Owen has many short-lived sexual relationships with women such as Suzie Costello and Gwen Cooper but remains largely indifferent to the affections of colleague Toshiko Sato. In Torchwood series 2, Owen is killed by Aaron Copley, and having been resurrected with alien technology is left in a state of living death; cheating death proves short-lived, as Owen is seemingly vaporised in a surge of radiation in the series 2 finale, "Exit Wounds".

Toshiko Sato, played by Japanese-born British actress Naoko Mori, is Torchwood Three's technical expert and computer specialist. The character first appeared in the Doctor Who episode "Aliens of London", although this experience was not mentioned in Torchwood until her final appearance in the episode "Exit Wounds", where it was revealed that she was covering for team medic Owen. Toshiko is quiet, fiercely private and professional. A fantastic genius, she was recruited into Torchwood after being imprisoned by a similar organization, UNIT, from whom she stole design plans for a "sonic modulator" in a bid to free her captured mother. Working for Torchwood Three, Toshiko perfected the "Rift Manipulator" device for the organization. Throughout the series, Toshiko is seen to harbor feelings for Owen Harper; she confesses the extent of her feelings on her death-bed as Owen laments never managing to take her on the date he promised her.

Ianto Jones, played by Welsh actor Gareth David-Lloyd, is Torchwood Three's support man. His job initially involves managing clean-up operations concerning Torchwood's various activities and providing tea and coffee, although his role later expands to accompanying the team on field missions. Having transferred to Torchwood Three from the head branch in London (Torchwood One), Ianto at first has the main motivation of simply housing his partially cyber-converted girlfriend Lisa Hallett, who later breaks loose and is exterminated by the team in "Cyberwoman". He enters into a sexual relationship with Jack in the first series, which meets with mixed reactions from the other characters; Owen, for example, characterizes him as Jack's "part time shag". Ianto never received full security in his relationship with Jack or with his sexuality; shortly after he became secure with their being labelled a "couple", he was killed by a virus in episode four of the 2009 serial Children of Earth.

Rhys Alun Williams, portrayed by Welsh actor Kai Owen, is a recurring character in the first two series and a main cast member from the third series onwards. Rhys is initially introduced as Gwen's oblivious live-in boyfriend, but as the series progresses he becomes aware of the existence of extraterrestrial life, and the true nature of Gwen's job. The two marry in the episode "Something Borrowed" and proclaim a relationship based on truth. When the government attempt to assassinate Gwen Cooper in Children of Earth, Rhys goes on the run with the team, assisting his wife in lieu of a fourth team member following the deaths of Tosh and Owen. Though he would rather live a domestic life with Gwen and their daughter Anwen in the fourth series, Rhys again finds himself having to assist Torchwood—which is no longer an official government agency, but rather a band of fugitives—over the course of the fourth series.