Human epidermal Langerhans cells (LCs) can coordinate both immunogenic and tolerogenic immune responses, creating an attractive opportunity for immunomodulation strategies. To investigate transcriptional determinants of human primary LC tolerance we applied single cells RNA-sequencing combined with extensive functional analysis. Unsupervised clustering of single cell transcriptomes indicated that steady-state LC populations exist in a spectrum of immune activation between two states: immunocompetent and immature, distinguishable by high or low CD86 expression, respectively. Suprisingly, LC immunompetency was critical for the efficient induction of regulatory T cells during co-culture assays with naive CD4+ T cells and expansion of autologous memory T cells. Consistently, LC tolerogenic potential was significantly enhanced upon migration from the epidermis. Transcriptional programmes underpinning LC immunocompetency, with increased expression of dendritic cell activation markers (CD83, HLA-DRA and CCR7), were complemented with expression of tolerogenic markers (IDO1, LGALS1 and AHR) in migrated LC. Using protein expression analysis and perturbation with inhibitors, we confirmed the role of IDO1 as a key regulator of LC tolerogenic responses induced during LC migration, identified AHR as a potential component of IDO1-regulatory feedback loop, and demonstrated LC-mediated tolerance can be modulated through treatment with dexamethasone, indicating an opportunity for targeted therapeutic interventions in inflammatory skin disease.