Mechanochemical reactions are performed to depolymerize organosolv lignin with sodium hydroxide in a mixer ball mill. GPC analysis reveals that rapid depolymerization into small oligomers occurs within minutes of milling time, followed by a slower reduction in average relative molecular mass over the next 8 h of milling. Monomeric products are identified by GC-MS and quantified by GC-FID. The extent of depolymerization appears to be limited by repolymerization reactions that form bonds between products. Suppression of these repolymerization reactions can be achieved through the addition of methanol as a scavenger or adjustment of the moisture content of the feedstock. These modifications result in lower average relative molecular masses and higher yields of monomers. These results are an important step towards designing an efficient pathway for lignin valorization.