Homogeneous colloidal dispersions of nitrogen-doped graphene in N,N-dimethyformamide (DMF) were readily prepared through a facile hydrazine-assisted solvothermal reduction method. The reduced graphene oxide (RGO) sample, prepared at a weight ratio of hydrazine to graphene oxide (GO) of 1.4 : 1 at 180 °C, was found to possess the highest conductivity (2716.2 S m⁻¹) and good dispersibility (0.5 mg mL⁻¹). This work has not only developed an efficient route to prepare high-quality graphene, but also provides a systematic elucidation of the reaction mechanism for the de-oxygenation of GO based on product characterization. It was found that all of the oxygen-containing groups were reduced by hydrazine-assisted solvothermal reduction. The deoxygenation of GO and re-establishment of the conjugated graphene network were significantly promoted by hydrazine de-epoxidation, a Wolff–Kishner–Huang-type reduction, as well as reactions between metastable NHNH₂ and hydroxyl groups. The ease of synthesis of nitrogen-doped RGO with both high conductivity and excellent dispersibility will greatly facilitate potential applications.