This study explores STEM doctoral student agency with respect to funding as it relates to degree completion and career preparation. We interviewed 39 graduate students in chemistry, physics, and engineering at two large, public, research-intensive institutions in the USA. Although STEM doctoral students have a high expectation of full funding, instability of funding and unavailability of desired funding types limit the agency of some students. When several types of funding are available, advisors can encourage student agency in pursuing opportunities to gain skills or networking connections through teaching assistantships, research assistantships, or internships. However, students were not able to articulate specific ways that assistantships prepared them for nonacademic positions, which is an important direction for future work.