Timotheus Vermeulen has long been a contributor to Frieze and regularly writes for other venues including Texte zur Kunst and Metropolis M. Among the artists whose shows he has reviewed are Gardar Eide Einarsson, Jill Mulleady, Eva LeWitt, Susan Philipsz, Sascha Weidner, Özlem Günyol & Mustafa Kunt, Elaine Sturtevant, Ilse D’Hollander, Katie Holten, Charlotte Posenenske, Jessica Warboys, Bettina Krieg, Jenny Michel, David Thorpe, Ane Mette Hol, Christoph Schellberg, Daiga Grantina, Christoph Knecht, Simon Evans, Oyvind Fahlstrom, David Douard, and Bernd Krauss. In his role as joint editor of the now defunct webzine Notes on metamodernism, he considered the oeuvres of artists including Sejla Kameric, Ragnar Kjartansson, Annabel Daou, Paula Doepfner, Guido van der Werve, David Lynch, Darren Almond, Haruki Murakami and Cyprien Gaillard.
Vermeulen is frequently invited to write exhibition and catalogue texts. Artists whose practice he has discussed in this context are Laure Provost, Eric van Hove, Diango Hernandez, Matthias Bitzer, Grit Richter, Esther Klas, Linda Matalon, Keith Tyson, Oscar Santillan, Sebastian Freytag, Ralf Brog, Korpys and Loffler, Peter Ewig, Michael Sailstorfer, Andy Hope 1930, Ulla von Brandenburg, Veronique Bourgoin, and Christoph Schellberg. Commissioning institutions include the MUHKA (Antwerp, Belgium), Bonner Kunstverein (Bonn, Germany), Stedelijk Museum (Amsterdam, the Netherlands), Kai10 (Dusseldorf, Germany), the Dortmunder Kunstverein (Dortmund, Germany), Witte de With (Rotterdam, the Netherlands), The Museo Universitario Arte Contemporáneo (Mexico City, Mexico), Museum of Art and Design (New York, USA), the Zabludowicz Collection (London, UK), Museum Morsbroich (Leverkusen, Germany), Landesmuseum (Linz, Austria).
In his role as a critic, Vermeulen has served on numerous committees and juries for art prizes, most recently Coast Contemporary, the Nam Jun Paik Award and the Bonner Kunstpreis. He also advises and consults on exhibitions and regularly teaches at art academies.