BACKGROUND Isobutyrate is a platform chemical that is currently produced from a non‐renewable fossil‐based feedstock. This study aimed at developing a renewable isobutyrate production process by using methanol chain elongation, a novel bioprocess that uses organic waste as primary feedstocks and an undefined reactor microbiome as the catalyst. RESULTS A continuous anaerobic bioreactor experiment was first performed using a synthetic medium containing acetate, butyrate and methanol, all of which are common derivatives from organic residues. Continuous isobutyrate (2.0 g L−1 day−1) and caproate formation (0.2 g L−1 day−1) from methanol, acetate and butyrate were demonstrated. A batch test to synthesise isobutyrate from a real organic waste, i.e. acidified supermarket waste (ASW), was performed. Up to 6.2 g L−1 isobutyrate was formed which accounted for 63% of all identified products. CONCLUSION In this study, a proof‐of‐principle for isobutyrate production from organic waste via methanol chain elongation was demonstrated. The continuous accumulation or supply of butyrate, the suppression of methanogenic activity and methanol addition were shown to be of use to provide conditions for isobutyrate formation. © 2016 Society of Chemical Industry