Electrochemical reduction of few-layer graphene oxide (FLGO) is a simple method for a partial restoration of sp2 network of the graphitic planes damaged by the previous oxidation/exfoliation process, and it is especially interesting for the in situ activation of FLGO in applications for energy conversion and storage. We present a detailed study of the structural evolution of FLGO and also non-oxidized graphene nanoplatelets (GNP) during electrochemical treatment. Two phases of the process can be traced tentatively in the case of FLGO by ex situ X-ray photoelectron spectroscopy and both ex situ and in situ Raman spectroscopy. The first phase is irreversible and dominated by a fast removal of oxygen-bearing functional groups accompanied by a structural ordering, while the second phase shows only a slow irreversible progressive reduction and the major changes in the Raman spectra caused by lattice expansion/contraction upon doping or a mild oxidation/reduction are reversible this time. In GNP, no irreversible reduction is observed, i.e. the first phase is absent, leaving only the reversible variations traceable in the Raman spectra.