Tema Milstein's work is in the field of environmental communication, a social science and humanities transdiscipline that understands communication as a powerful force at a time of human-generated ecological and climatic crises. She is particularly known for cultural approaches to studying how communication shapes ecological understandings, identities, and actions. Her work tends to discourses that otherwise go unnoticed, to connections between discourses and wider destructive or restorative practices, and to paths toward sustainable, just, and regenerative futures. Her research spans the globe, illustrating tensions between overarching and marginalised environmental meaning systems, examining ecotourism and environmental activism, and establishing the study of ecocultural identities. Milstein's Routledge Handbook of Ecocultural Identity (Routledge, 2020, co-editor José Castro-Sotomayor) gathers 40 international interdisciplinary authors to bring the ecological turn to sociocultural understandings of the self. She is a former Fulbright Scholar and is the 2020 recipient of the Faculty of Arts, Design, and Architecture Dean's Research Award for Society Impact. 

As a member of the Environment & Society Group, Milstein serves as convenor of the Master of Environmental Management, a program focused on nourishing tomorrow's change-makers in restoratively rethinking and reshaping the world. She is dedicated to transformative ecopedagogy, and is co-editor of Environmental Communication Pedagogy and Practice (Routledge, 2017), founder of the "inside-out classroom," and served as her former institution's University Presidential Teaching Fellow. Milstein has taught at universities in Australia, the United States, Italy, China, and New Zealand. Before coming to UNSW, she was associate professor of Geography & Environmental Studies and Environmental Communication at the University of New Mexico. In her previous professional life, she was a print and public radio journalist.

At UNSW, she is involved in several projects, including as co-lead for (Daily) Delight~Disrupt, a research-informed public movement project to ignite everyday experiences of ecocentric transformation (affiliated with the global Massive Change Network). She's a founding member of UNSW's Regenerative Response Collective, serves as Advisory Committee member for UNSW's Fowlers Gap Research Station, as Reference Group member for UNSW's Institute for Industrial Decarbonisation, and as member of Beyond Growth, a UNSW staff-formed group.

Internationally, Milstein is Conference Chair for the International Environmental Communication Association (IECA) 2025 Conference on Communication and Environment, which will convene for the first time in the southern hemisphere (Tasmania). She also serves on several journal editorial boards, including flagship journals in the field such as Environmental Communication, the Quarterly Journal of Speech, and Communication Monographs.