This study aims to formulate biscuits incorporating gluten-free millet flour. The wheat flour was substituted by millet flour at various ratios of 10%, 20%, and 30% (w/w). The physical properties, the proximate composition, and antioxidant activity, including consumer acceptability, were evaluated. The results revealed a significant increase 2-fold in fibre content with slightly increased ash content. Biscuit diameter increased when millet flour increased due to less effect of gluten, relative to increased spread factor. In addition, the biscuit containing 30% millet flour had the darkest colour surface, and its texture was easy to break. There was an increase in the total phenolic content (4.76 mg GAE/g) and antioxidant activity also increased to 5.67 µmol TE/g, and 13.60 µmol TE/g as measured by DPPH and ABTS assays, respectively. These improved the nutritional values of biscuits when substituted with millet flour at 30%. Furthermore, the most consumer acceptability was observed for the biscuits substituted at this level. Thus, millet flour can be used to substitute wheat flour at 30% in the development of nutritional butter biscuits.