Common buckwheat flour (BF) was used to substitute 10%, 20%, 30% and 40% of corn starch, the main component of a gluten-free bread formula, to make buckwheat-enhanced gluten-free breads. The 40% BF-enhanced gluten-free bread showed the highest antioxidant capacity against ABTS+˙ and DPPH˙ radicals (4.1 and 2.5 μmol Trolox g−1 DM, respectively) and reducing capacity measured by cyclic voltammetry (1.5 μmol Trolox g−1 DM). The antioxidant and reducing capacity of buckwheat-enhanced gluten-free breads were positively correlated with their total phenolic contents (r = 0.97). The 40% BF-enhanced gluten-free bread showed the highest overall sensory quality (7.1 units) when compared to control gluten-free bread (1.8 units). The linear relationship between applied increasing BF doses in gluten-free bread formula and magnesium, phosphorus and potassium content in breads was noted. It was concluded that 40% BF-enhanced gluten-free bread could be developed and dedicated to those people suffering from coeliac disease.