Critical Theory pioneered the theorization of human-animal relations, helping establish that agency extends beyond the human world. Nonhuman agency is now widely accepted within the “new materialisms” and beyond but there are growing calls for more critical approaches that consider why and how such agency is mobilized. These calls effectively bring together the concerns of “old” and “new” materialisms. I therefore return to Critical Theory, bringing its explanatory analysis, practical framework and future imaginary into conversation with more recent research into nonhuman agency. Together, they reveal how the relations between human and nonhuman actors shape and are shaped by their broader socio-political context. I suggest that paying closer attention to human-domestic animal relations in particular might help us resolve some of the issues at stake. Consequently, for illustrations to extend the analysis, the article turns to horses, a nonhuman group who occupy a unique place in our collective unconscious.