We have shown a sustainable photocatalytic depolymerization strategy converting soda pulped lignin (SL) mainly into guaiacyl alcohol. In order to understand the reaction mechanism, photocatalytic reaction between model compound (2-PAP) and PAB was investigated using real-time NMR. LC-HRMS spectra and SEC traces of photocatalytically depolymerized products highlighted the successful bond cleavage, i.e. unzipping of the polymeric structure. Photoconversion of soda lignin to monomers/oligomers that are rich in carbonyl functionalities supported our proposed mechanism of the model compound reaction in which the consumption of β-O-4 motifs led to the formation of carbonyl containing species. The unprecedented catalytic performance of PAB toward inducing β-O-4 scissions can be qualitatively rationalized by formation of photolabile brominated compounds and by invoking the generation of phenacyl radical within the lignin, causing the subsequent breakdown. The initially formed brominated lignin moieties result in the inhibition of aggregation and condensation of lignin, leading to significant increase of solubility. Furthermore, generation of HBr should play synergistic influence on the photocatalyzed depolymerization process through demethylation/phenolation. In short, the critical advancement of this work is the demonstration of a novel approach for technical lignin valorization under mild conditions. We believe that our disclosed photocatalytic method can provide intrinsic insights into the depolymerization of lignin. The depolymerization method presented here underlines the potential of simple, metal-free, in-situ and sustainable photocatalytic systems for the efficient transformation of technical lignins into valuable aromatics under mild reaction conditions.