Tuomas Heikkilä (b. 1972), PhD, docent in general history and and church history (University of Helsinki) and docent in Finnish history (University of Turku), is one of the most influential Finnish medievalists. Currently employed at the University of Helsinki as the Professor in Church History, he has previously been the Director of the Finnish research institute in Rome, Italy, (2013-2017); Visiting Research Fellow at the Swedish Collegium for Advanced Study (2010); and Visiting Scholar at the University of Gothenburg (2009).

Heikkilä's almae matres are the University of Helsinki, the Eberhard-Karls-Universität Tübingen, Germany, as well as the Biblioteca Apostolica Vaticana where he took the European Diploma in Medieval Studies. 

Originally a historian, Heikkilä has emphasized multidisciplinary scholarship. His fields of expertise include written culture and the change of information environment, medieval hagiography, manuscript studies, monastic history, and computer-assisted stemmatology. Heikkilä has published widely on these topics in several languages.

Heikkilä wrote his doctoral thesis (Vita et miracula s. Symeonis Treverensis – ein hochmittelalterlicher Heiligenkult im Kontext, Academia Scientiarum Fennica 2002) on high medieval hagiography in Western Europe. Later on, he expanded his expertise to include Nordic hagiography and edited the legend of St Henry, the Finnish national saint. The studies resulted in monographs in Finnish and Swedish as well as the first critical edition of the oldest literary work composed in Finland.

In 2006–2011, Heikkilä directed a large-scale research project on the arrival and development of written culture in Finland. The project resulted in a detailed picture of the implications of Latin written culture in a European periphery as well as a research database of the fragmenta membranea collection of the National Library of Finland. Heikkilä has also been one of the driving forces behind the two other Finnish databases on medieval sources: the Diplomatarium Fennicum and the Codices Fennici.

In 2009–2012, Tuomas Heikkilä directed Studia Stemmatologica, an international multidisciplinary scholarly network concentrating on exploring the possibilities and different uses of computer-assisted stemmatology.

In 2013-2017, Heikkilä was the director of the oldest and most prestigious Finnish scholarly institute abroad, Institutum Romanum Finlandiae. In Rome, Heikkilä's research group concentrated on the study of different aspects of time and calendars in the Middle Ages and the Renaissance.