Transcription-coupled DNA repair (TCR) removes transcription-blocking DNA lesions through the coordinated assembly of repair factors on arrested RNA polymerase II (Pol II). This process requires the site-specific ubiquitylation of Pol II by the CRL4CSA ubiquitin ligase. Pol II ubiquitylation is facilitated by ELOF1, a recently identified TCR factor. Using cryogenic electron microscopy, biochemical assays, and cell biology, we reveal that ELOF1 functions as an adaptor to correctly dock CRL4CSA onto Pol II and facilitate the recruitment of UVSSA. The ELOF1-CSA-UVSSA interaction positions CRL4CSA on arrested Pol II, leading to its ubiquitylation upon ligase activation by neddylation. ELOF1-mediated repositioning enables a TFIIS-like element in UVSSA to reach the Pol II active site and the pore region to prevent Pol II re-activation. These findings provide the structural and molecular basis underlying the transition of Pol II from a transcriptionally active to an arrested state, primed for DNA repair.