Janet Marion Leathem is a New Zealand psychology academic specializing in traumatic brain injury. She is currently a full professor at Massey University.

After a 1975 MSc thesis titled 'The assessment of laterality' and a 1980 PhD titled 'Some Aspects of Cortical Functioning in Man,' both at Victoria University of Wellington, Leathem moved to Massey University, where she rose to full professor.

Leathem has spoken out about memory loss, in relation to the John Banks and Kim Dotcom scandal, and the way concussion is handled in rugby union.