<p>There is an ever-growing interest in the thermochemical conversion of biomass into functional porous chars. This is driven by their efficiency in timely applications in agriculture, medicine, water treatment, and energy storage, therefore addressing numerous sustainable development goals. This study concerns the valorization of millet bran into functional chars. This biomass constitutes the fibrous outer layer enveloping the millet seed, a cereal widely cultivated in Senegal. It was separated from the flour by sieving or sifting before conversion into chars. The latter was pyrolyzed (P) in the 400–900&#xa0;°C range to provide biochar samples, or hydrothermally treated at 300&#xa0;°C to yield hydrochar (H300). This material was further post-pyrolyzed (300–900&#xa0;°C) to yield pyro-hydrochars. The chars were characterized by Raman spectroscopy, X-ray diffraction, X-ray electron spectroscopy, and cyclic voltammetry. Raman studies showed that the biochars obtained at 400 and 500&#xa0;°C (P400 and P500), hydrochar (H300), and the pyro-hydrochar (H300-P300) are the most graphitized, as judged from the D/G peak intensity ratio. These results were confirmed by cyclic voltammetry demonstrating that these products have the best redox properties, i.e. high current (10 µA for 0.1&#xa0;mg) and lowest peak potential difference ΔE of 0.18&#xa0;V for P400. The remarkable electroactive properties of P400 correlate with its lowest Raman I_D/I_G peak intensity, and surface atomic O/C ratios, respectively. As the most electroactive char, P400 was further as electrode material for detecting heavy metal ions, in phosphate buffer solution (pH 4), by differential pulse voltammetry (DPV). The detection limits were 0.100 and 0.108 µΜ, for Pb²⁺ and Cu²⁺, respectively. This work demonstrates the possibility of developing electroactive chars for environmental monitoring of pollutants, provided the carbonization conditions of the initial biomass are tuned.</p>