Gene regulatory mechanisms that modulate RNA Polymerase II activity are difficult to access in mammalian tissues composed of multiple cell lineages. Here, we develop a nascent RNA assay (PReCIS-seq) that measures lineage-specific transcriptionally-engaged Pol II on genes and DNA enhancer elements in intact mouse tissue. By employing keratinocytes as a prototype lineage, we unearth Pol II promoter-recruitment versus pause-release mechanisms operating in adult skin homeostasis. Moreover, we relate active enhancer proximity and transcription factor binding motifs on promoters to Pol II activity and promoter-proximal pausing level. Finally, we find Pol II firing rapidly into elongation on lineage identity genes and highly paused on cellular safeguarding genes in a context-dependent manner. Our work provides a basic platform to investigate mechanistic principles of gene regulation in individual lineages of complex mammalian tissues.