[17][18] In 2012, Tannahill and his then-boyfriend William Ellis founded and ran Videofag, an alternative arts space operated out of a defunct barbershop in Toronto's Kensington Market.
[19][20] Tannahill's debut novel, Liminal, published in 2018, is a work of autofiction which follows the author as he reckons with the nature of consciousness and the abject, precipitated by the sight of his mother's sleeping - or possibly dead - body.
[21] In her review of the novel, Martha Schabas of The Globe and Mail wrote "Tannahill's lushly intelligent debut... captures something illuminating and undefinable about the present moment; it speaks in the code and cadences of the late 2010s and paints an incisive portrait of the demographic we call millennial", and compared it to the work of authors Ben Lerner, Rachel Cusk and Karl Ove Knausgaard.
[25] In their citation, the Giller jury called the novel "a masterful interrogation of the body, as well as the desperate violence that undergirds our lives in the era of social media, conspiracies, isolation and environmental degradation.
"[29] Tannahill adapted his novel into a limited series, produced by Element Pictures for the BBC, directed by Janicza Bravo and starring Rebecca Hall.
[43] The collection features three plays for solo performers: Get Yourself Home Skyler James, the true story of a young female soldier who deserts the American military, the live-streamed monologue rihannaboi95, about the fallout from a queer teenager's viral video, and Peter Fechter: 59 Minutes, which imagines the final hour in the life of Peter Fechter, an adolescent from East Berlin shot while attempting to cross the Berlin Wall in 1962.
An early example of virtual theatre, rihannaboi95 was performed nightly in a bedroom over live-stream video in 2013, and won a Dora Mavor Moore Award for 'Outstanding New Play for Young Audiences.
'[44] Tannahill's play Late Company, about two sets of parents seeking closure after a tragedy involving their sons, premiered at the 2014 SummerWorks Festival in Toronto, and went on to receive multiple productions across Canada, and abroad.
[49] Concord Floral, a play written by Tannahill, and developed and directed by Erin Brubacher and Cara Spooner over a three-year process involving Toronto-area teenagers, is a reimagining of Giovanni Boccaccio's The Decameron as a contemporary suburban ghost story.
The fragmentary and lyrical play, inspired by the terminal illness of the playwright's mother, was described by Karen Fricker of The Toronto Star as "a devastating but joyous statement about life and grief.
Developed and directed by Erin Brubacher, in collaboration with ensembles of teenagers from Düsseldorf and Toronto, the play premiered at the 2022 Theater der Welt, before productions in Canada, Germany, Sweden, and as part of the 2023 National Theatre Connections festival in London.
It was announced by Playbill in 2024 that Tannahill's play Prince Faggot will have its world premiere Off-Broadway at Playwrights Horizons, in a co-production with Soho Rep, in spring 2025.
[59] Tannahill's work in contemporary dance includes choreographing and performing with Christopher House in Marienbad for the Toronto Dance Theatre in 2016; and writing the text for Xenos in 2018, and Outwitting the Devil in 2019, two shows by choreographer Akram Khan, which have toured internationally to venues including Sadler's Wells Theatre, Festival d'Avignon, and the Lincoln Center for the Performing Arts.