We evaluated health workers' perspectives on the implementation of the 2016 HIV "Test and Treat" guidelines in Nigeria. Using semi-structured interviews, qualitative data was collected from twenty health workers meeting inclusion criteria in six study sites. Data exploration was conducted using thematic content analysis. Participants perceived that the "Test and Treat" guidelines improved care for PLHIV, though they also perceived possible congested clinics. Perceived key factors enabling guidelines use were perceived patient benefits, availability of policy document and trainings. Perceived key barriers to guidelines use were poverty among patients, inadequate human resources and stock-outs of HIV testing kits. Further improvements in uptake of guidelines could be achieved by effecting an efficient supply chain system for HIV testing kits, and improved guidelines distribution and capacity building prior to implementation. Additionally, implementing differentiated approaches that decongest clinics, and programs that economically empower patients, could improve guidelines use, as Nigeria scales "Test and Treat" nationwide.