<p>This study aims to fill in the gaps in the experiment-based fundamental knowledge on the interaction of graphene and polyaniline at the “molecular” level, namely, charge redistribution and nature of charge carriers in polyaniline. We synthesized a two-dimensional graphene/polyaniline heterostructure and studied electronic structure and interactions of its components. The charge-transfer measurements showed that the formed polyaniline acts as a <i>p</i>-type dopant of graphene: the graphene electrons are accepted by polyaniline within the Fermi level alignment process. Raman and XPS spectroscopies and Raman spectroelectrochemistry on the (¹³C–)graphene/polyaniline interface reveal that the majority of polyaniline is in the polaron lattice form and a minority in the bipolaronic form. The XPS data show that the number of polyaniline charged nitrogen atoms exceeds the number of counter-anions, indicating that the proton doping of polyaniline as the main mechanism of polaron formation/stabilization is accompanied by a second mechanism, in which polarons and bipolarons are stabilized by graphene electrons in a mutual interaction. The work provides essential knowledge needed for a rational design of graphene/polyaniline nanocomposites and their exploitation in various devices.</p> Graphical Abstract <p></p>