Fiber-based elements are commonly used to simulate steel beam-columns, due to their ability to capture P-M interactions and spread-of-plasticity. However, when mechanisms such as local buckling result in effective softening at the fiber-scale, conventional fiber models exhibit mesh dependence. To address this, a two-dimensional nonlocal fiber-based beam-column model is developed and implemented numerically. The model focuses on hot-rolled wide flange (W-) sections that exhibit local buckling-induced softening when subjected to combinations of axial compression and flexure. The formulation up-scales a previously developed nonlocal formulation for "single-fiber" buckling to the full frame element. The formulation incorporates a physical length scale associated with local buckling, along with an effective softening constitutive relationship at the fiber level. To support these aspects of the model, 43 Continuum Finite Element (CFE) test-problems are constructed. These test-problems examine a range of parameters including the axial load, cross-section, and moment gradient. The implemented formulation is validated against CFE models as well as physical steel beam-column experiments that exhibit local bucklinginduced softening. The formulation successfully predicts post-peak response for these validation cases in a mesh-independent manner, while also capturing the effects of P-M interactions and moment gradient. To enable convenient generalization, guidelines for calibration and selection of the model parameters are provided. Limitations are discussed along with areas for future development.