Organic solid waste is one of the most promising feedstocks for the implementation of the circular economy principles in waste management. Its anaerobic treatment can indeed promote organic matter conversion into a number of value-added products as well as energy carriers. However, the identification of sustainable strategies to handle organic solid waste in a biorefinery framework still poses technological as well as economic challenges. The aim of this study was in enhancing the potential of the organic fraction of municipal solid waste (OFMSW) to produce bioenergy and biochemicals by combining dark fermentation with a formic acid pretreatment. Hydrogen yields up to 31.6 ml/g VS were obtained pre-treating the OFMSW with 5% formic acid, at 80 °C for 70 min. Concomitantly, a wide range of metabolites of market significance, including acetic acid, butyric acid and ethanol, accumulated. The concentration of these metabolites further enhanced after the dark fermentation of the pretreated substrates. Experimental tests highlighted the influence of the different pretreatment operating conditions on the relative production of hydrogen and main metabolites as well as the related pathways. It was found that the acid concentration plays a key role in promoting the biological conversion of OFMSW and that the adjustment of the operating temperature and treatment time can be targeted towards the production of either building blocks or energy carriers, so as to ensure the viability of the process for its scale up.