Universal antiretroviral therapy (ART) strategies have dramatically changed HIV programming across sub-Saharan Africa. We explored factors that influenced the development, adoption and implementation of universal ART policies in Tanzania, South Africa and Malawi. We conducted 26 key informant interviews and applied Kingdon's 'streams' model to explore how problems, policies and politics converged to provide a window of opportunity for universal ART roll-out. Weak health systems and sub-optimal care retention were raised as problems during Option B+ implementation, which preceded universal ART , and persisted after its implementation. The adoption and implementation of Option B+ policy facilitated the uptake of universal ART. Politics played out through pressures from different stakeholders to accelerate or slow down implementation, from governments, civil society groups, researchers and donors. Policy processes leading to universal ART were open to pressures and influence. The extraordinary financial support which enabled the widespread and rapid implementation of universal ART skewed the power balance and sometimes left little space for locally-derived solutions to respond to specific health system abilities and epidemiological contexts. Donors may be more effective if they ensure a greater focus on strengthening the whole health system as well as accounting for local contextual factors and recent policy development histories when funding policy implementation.