Hierarchical carbons with different boron contents (from 0.42 to 2.37 wt.%) were prepared by combination of soft-templating and hydrothermal approaches. This newly developed strategy enables adequate control of the chemical state of the boron functionalities in carbon materials since the self-generated pressures favour B–C bond formation. The total content of oxygen increases simultaneously with the boron content, and its speciation is also influenced by the boron chemical state distribution: the presence of C–B–C (BC3 and BC2O) species induces the oxidation of phenols to carbonyls. The electrochemical performance of the prepared carbons was tested in a three-electrode cell configuration (1 M H2SO4) showing good specific capacitances per BET specific surface area (20–36 μF/cm2). The presence of boron on the carbon backbone improves both the charge propagation and the pseudocapacitive properties. Nevertheless, the electrochemical properties are only enhanced up to some level of boron doping (around 1.8 wt.%). A two-electrode supercapacitor built with a carbon prepared by a mild hydrothermal synthesis (50 °C during 28 h) delivered energy densities similar to those of commercial activated carbons. This could lead to high volumetric capacitance, since the boron doped carbons present much higher density.