The mechanical behaviour and design of fixed-ended unequal-leg angle section steel members subjected to axial compression are studied herein. The mechanical response of unequal-leg angle section columns is first described, with a particular emphasis on the relationship between torsional and local buckling, alongside the important transition from equal-leg to unequal-leg angle behaviour. Existing experimental data on unequal-leg angle section steel columns are then employed to validate numerical models developed within the commercial finite element package ABAQUS. A comprehensive parametric study is subsequently conducted that encompasses a broad spectrum of geometric configurations and global slenderness values. The mechanical behaviour and ultimate resistance of fixed-ended unequal-leg angle section columns are shown to be dependent on not only the global slenderness, but also on the ratio of the elastic torsional-flexural to minor-axis flexural buckling loads. The existing experimental data alongside the numerical parametric study results are employed to evaluate the resistance predictions given by the current Eurocode 3 design provisions, revealing an excessive level of conservatism. Finally, a new design approach for fixed-ended unequal-leg angle section steel columns, suitable for incorporation into future revisions of Eurocode 3, is proposed that significantly improves the accuracy and consistency of the resistance predictions. A reliability analysis of the proposed design approach is conducted in accordance with the procedure within EN 1990, resulting in a recommended partial safety factor γ_M₁=1.0.