Varnavas is situated in the hills of northeastern Attica. The main land use is agriculture. The nearest towns are Kapandriti (4 km west) and Grammatiko (4 km southeast). It is 8 km northwest of Marathon and 32 km northeast of Athens. Landmarks include the Historic People's Museum of Varnavas (Istoriko Laografiko Mouseio Varnava).
The municipal unit has a land area of 37.349 km2 (14 sq mi) and a total population of 2,081 inhabitants (2011). Its other settlements are Agía Paraskeví (pop. 244), Ágioi Dimítrios kai Panteleímon (189), Moní Metamorfóseos Sotíros (136), Ágios Ioánnis (81), Pouríthi (66), Moní Panagías (32), and Limniónas (7).