Transitional justice institutions are popular tools for addressing past human rights violations in post-conflict societies, but they often operate under intense political pressure. We argue that, while striving for impartiality, actors in these institutions face strong incentives to favor incumbents - especially in politically unstable contexts. We explore this tension using a unique dataset of amnesty decisions from the South African Truth and Reconciliation Commission (1996–2001), the only transitional justice institution to have released comprehensive records of its decisions. Our analysis reveals a consistent pattern of favoritism toward members of the incumbent African National Congress (ANC), alongside systematic bias against their political rivals, the Inkatha Freedom Party (IFP). Results are robust to controlling dynamically for all features of the cases and are unlikely to be driven by unobserved variables. Notably, no such favoritism extended to other anti-apartheid organizations, nor did we find higher rejection rates among former apartheid officials. We explore mechanisms behind our results. On the demand side, ANC control over appointments during later expansions of the judging panel led to the inclusion of politically aligned judges. On the supply side, career ambitions played a role: judges who exhibited bias were more likely to pursue higher judicial or political positions after their TRC service. Qualitative evidence from hearing transcripts reveals that IFP members faced systematically higher evidentiary standards than ANC members for comparable offenses. Our findings highlight the importance of multiparty involvement in appointing transitional justice officials and provide rare insights into the behavior of transitional justice institutions.