The deep structure of the northern North Sea and the adjacent Norwegian mainland has been analysed by integrating all available structural data in combination with 3D density and magnetic modelling into a lithosphere-scale 3D structural model. The modelled configurations of the sedimentary cover and crystalline crust are consistent with the long-wavelength components of the observed gravity and magnetic fields over the study area. The first-order configurations of the top of the crystalline basement and the Moho topography have been obtained. According to the 3D density modelling, the low-density upper-crustal block beneath the Horda Platform has been shown to indicate a possible presence of metasedimentary and/or fractured granitic rocks. Possible remnants of island arc chains within the central part of the North Sea between the Laurentian and Baltican crustal domains are supported by the modelling. Moreover, based on the results of the 3D magnetic modelling, the 3D density/structural model has been differentiated into smaller crustal blocks with different magnetic properties, implying that these magnetically derived crustal blocks most likely differ lithologically from the rest of the initial density-based larger layers. Within the mainland, most of the crustal blocks with increased magnetic susceptibility are related to granitic and/or granodioritic rocks which are well mapped at the surface according to geological data. A prominent middle–upper crustal magmatic intrusion has been modelled within the northern part of the Norwegian– Danish Basin. The local magnetic pattern supports a possible Permian age for this intrusion, whereas the regional magnetic pattern and known geology from the mainland indicate a Sveconorwegian origin as a more viable alternative. At the mantle level, a low-density lithospheric mantle has been modelled beneath NW Norway and adjacent offshore areas, reflecting the likely presence of an upper-mantle low-velocity zone there.