Late Jurassic – Early Cretaceous global carbon-cycle dynamics have mainly been inferred from Tethyan, Atlantic and Pacific carbon-isotope (δ¹³C) records. These records indicate a steady deceleration of the carbon cycle in Late Jurassic and Jurassic–Cretaceous (J–K) boundary times followed by a major mid-Valanginian carbon-cycle perturbation demarcated by the well-documented positive excursion named the Weissert Event. However, this model remains to be confirmed in Boreal records, which are rare and typically difficult to correlate with the global δ¹³C signal. In this study, the first continuous and biostratigraphically calibrated organic carbon-isotope (δ¹³C_org) stratigraphy is established for the Bathonian – lower Barremian (representing >30 Myr) of the Boreal Realm, based on high-resolution sampling of bulk-rock marine shale from four time-equivalent sections in Arctic Svalbard, supplemented by existing δ¹³C_org data. The δ¹³C_org stratigraphy displays several distinctive trends, notably: (i) a Kimmeridgian positive excursion, followed by a large negative excursion (≤6.4‰) in the upper Kimmeridgian – middle Volgian, consistent with existing Boreal δ¹³C records; (ii) an upper Volgian – Ryazanian overall positive recovery across the J–K boundary; and (iii) a prominent positive excursion (≤5.5‰) in the Valanginian, interpreted to represent the Weissert Event, followed by steady, high values into the lower Barremian with no apparent excursion decay. Time-calibrated correlation of the observed trends with existing δ¹³C records representative of the entire exchangeable carbon reservoir reflects major global carbon-cycle adjustments, including: (i) Boreal decoupling from the global carbon reservoir during Late Jurassic and J–K boundary times due to basinal isolation; and (ii) global carbon-cycle recoupling at the onset of the Weissert Event coinciding with incipient oceanographic connectivity. Boreal carbon cycling was inherently controlled by the basin configuration. The new δ¹³C_org stratigraphy provides a well-calibrated tool for Boreal and Boreal–Tethyan correlations, and confirms that the Weissert Event represents an important perturbation of the global carbon cycle.