Fahrig studies effects of landscape structure—the arrangement of forests, wetlands, roads, cities, and farmland—on wildlife populations and biodiversity, [1] and is best known for her work on habitat fragmentation.

[4] She completed her PhD in 1987 at the University of Toronto under the supervision of Jyri Paloheimo, on the effects of animal dispersal behaviour on the relationship between population size and habitat spatial arrangement.

[5] After her PhD, Fahrig worked for two years as a postdoctoral fellow at the University of Virginia, researching how different plant dispersal strategies allow species to respond to environmental disturbances.

[7] In 1991 she joined the faculty of the Biology Department at Carleton University,[8] Ottawa, where, as of 2024, she is a Chancellor's Professor and the Gray Merriam Chair in Landscape Ecology.

Based on her MSc thesis in 1983,[4] Fahrig and Merriam published the first paper on habitat connectivity., [22] and provided the earliest evidence for the concept of wildlife movement corridors.

[28][29] Fahrig and her students found that the groups of species whose populations are most impacted by roads are amphibians, reptiles, and mammals with low reproductive rates.