Translesion synthesis (TLS) alleviates replication stalling at DNA lesions. Ring-shaped processivity clamps play a critical but ill-defined role in mediating exchange between replicative and TLS DNA polymerases at sites of DNA damage. We have developed a single-molecule approach to reconstitute TLS and exchange of the Escherichia coli replicative polymerase, Pol III, with the TLS polymerases Pol II and Pol IV. We observe clamp-mediated exchange of Pol III with both TLS polymerases, and that distinct sets of interactions of each polymerase with the clamp govern the mode of exchange. These results suggest polymerase selection is not simply governed by a mass action competition, but also by positioning of polymerases on clamps at replication intermediates, suggesting a hierarchy for access to DNA lesions.