A novel method for nitrogen doping of graphene via solid-state impregnation was developed using graphene oxide (GO) as the raw substrate and aminoterephthalic acid as the doping agent via a facile thermal treatment at 750 °C. The structure, morphology and chemical composition of the synthesised N-doped graphene were characterised using XRD, SEM, EDS and XPS. The N-graphene product exhibits homogeneous doping with high nitrogen content (∼6 at%) in four configurations: pyridinic-N, pyrrolic-N, pyridinic-N-oxide and graphitic-N. The electric double layer capacitor (EDLC) fabricated using an N-doped graphene electrode attained a specific capacitance of 210 F g-1 (at a current density of 1 A g-1), which was greater than the values attained by pristine graphene and a GO electrode by factors of about two and six, respectively. Our synthesised N-graphene shows supercapacitance at a low electrolyte concentration compared to supercapacitors reported in the literature for high electrolyte concentrations with similar electrodes. The EDLC device we constructed based on N-graphene showed excellent charge-discharge stability for tests of up to 5000 cycles with high capacity retention (>90%). A comparison of the electrochemical performance of GO, graphene and N-graphene demonstrated that doping with nitrogen can dramatically enhance capacitance.