The tectonic evolution of highly oblique continental margins that result from back-arc extension above lithospheric STEP faults is poorly understood. Here, we investigate the case of the Alboran margin in the eastern Betics characterized by crustal thinning of 15–10 km, oblique to the direction of slab retreat. The current deformation patterns indicate that oblique back-arc rifting is underway. However, it is unclear whether these conditions are those that prevailed during the formation of the metamorphic domes and intramontane basins. We review the temporal and spatial evolution of Neogene sedimentary basins and brittle deformation in the eastern Betics, and exploit offshore seismic reflection lines to propose a crustal-scale section across the oblique margin. The history of sediment infill and rates of subsidence combined with the analyses of fault slip data, confirm that brittle extension oriented from N20° E to EW occurred during an interval spanning from the Serravallian-early Tortonian to the late Tortonian (14–8 Ma). This extension is found associated with both normal and strike-slip regimes and the evolution of the strike-slip corridors flanking the metamorphic domes. The transtensional model forms a coherent scheme linking the ductile deformation associated with metamorphic domes and the formation of EW- and NW-SE/NNW-SSE-directed sedimentary basins in the brittle upper crust during the Tortonian. The oblique extension, which is closely associated with STEP faulting, occurred during the regional convergence between Africa and Iberia since the Miocene. Only recently, around 8 Ma, the slab detached, leading to local tectonic inversion. Such a type of narrow oblique rifted margin associated with transform-like plate boundaries is not unique but is expected to be hardly preserved in the geological record due to the transient nature of retreating subduction systems.