This dissertation examines the complete oeuvre of contemporary installation artist Robert Irwin from his early work in the 1950s to the present day. The first chapter considers his early paintings as well as his early sculptural objects, including his discs and acrylic columns made from 1968-70. The chapter considers the extent to which these works depart from the models of transcendence and interiority exemplified in late modernist painting. This analysis draws on recent writing in new materialist theory to challenge prevailing historiographic models that describe Irwin's interest in light and space as inferior to more "material" minimalist sculpture being made in New York City at the same moment. The second chapter includes Irwin's installation works for art museum and gallery spaces from 1970-2016, particularly his 1973 installations at the Panza Stables in Varese, Italy. This chapter considers the nature of the subject in Irwin's work, arguing that his installation pieces create a new, contingent model of human subjectivity that reflects contemporary developments in post-structuralist and new materialist theory. The final chapter examines Irwin's works for public and outdoor spaces from the early 1980s to the present day. This chapter considers whether Irwin's public works embrace or resist a spectacular mode of art viewing and consumption shaped by late capitalist aesthetics. In addition to a critical rehabilitation of Irwin's work, the dissertation concludes with a broader discussion about the nature of "critical" or politically progressive art at the turn of the 21st century, and about the limitations of earlier interpretive models that art historians have used to create hierarchies of value for postwar sculpture and installation art.