Proteolytic processing of the retroviral Pol polyprotein precursor produces protease (PR), reverse transcriptase (RT), and integrase (IN), except in foamy viruses (FVs) where only the IN domain is released. Here, we report the 2.9 Å resolution crystal structure of the mature PR-RT from prototype FV (PFV) needed for processing and reverse transcription. The monomeric PFV PR exhibits similar architecture as the HIV-1 PR but the N- and C-terminal residues are unstructured. A C-terminal extension of the PR folds into two helices that supports the RT palm subdomain and anchors the PR next to the RT. The subdomains of RT: fingers, palm, thumb, and connection, and the RNase H domain, are connected by flexible linkers and spatially arranged similarly to those in the HIV-1 RT p51 subunit. Significant spatial and conformational domain rearrangements are required for nucleic acid binding. This offers structural insight into retroviral RT conformational maturation and architecture of immature enzymes.