Lignin is the most abundant source of renewable aromatics on Earth, but its tendency to undergo irreversible condensation reactions during lignocellulose pretreatment hampers its valorization in current biorefinery schemes. An attractive strategy that allows to overcome this issue is the so-called reductive catalytic fractionation (RCF), which relies on the use of heterogeneous redox catalysts and hydrogen gas to promote the reductive cleavage of lignin and to prevent the occurrence of condensation reactions, ultimately yielding stable low-molecular weight phenolics, along with a delignified (hemi)cellulose fraction. Currently, a few limitations still exist that should be overcome to improve the potential of RCF. The treatment of lignocellulosic feedstocks alternative to the widely explored virgin woody biomass is of primary importance for extending the range of applications of this method. In addition, the recurrent adoption of high pressures of hydrogen gas undeniably poses safety and equipment constraints. With the goal of responding to these challenges, the RCF of abundantly available and inexpensive wheat straw biomass was investigated in this dissertation. The results obtained show that the RCF of wheat straw produces a depolymerized lignin oil comprising valuable phenolic monomers. The process could be performed in the absence of hydrogen gas, with the solvent acting as a hydrogen donor, at the expense of a less effective depolymerization of lignin. However, the treatment of heterogeneous feedstocks was identified as a potential problem for the catalyst stability. As an alternative to RCF, a novel method for the reductive depolymerization of lignin during biomass pretreatment was developed in this dissertation, based on the use of sodium dithionite as a soluble reducing agent. This method advantageously circumvents the need of hydrogen gas and precious metal catalysts. Such dithionite-assisted organosolv fractionation (DAOF) was shown to effectively promote the formation of low-molecular weight phenolics from lignin, while concomitantly yielding a processable cellulosic pulp. A techno-economic assessment of DAOF highlighted that this method can be economically viable. Furthermore, DAOF was demonstrated to be a flexible method with respect to the treatment of different lignocellulosic feedstocks. While the selection of the most suitable pretreatment will ultimately depend on the biomass properties, on the desired features of product streams, and on technical and economic constraints of the biorefinery, this dissertation shows that both RCF and DAOF represent promising approaches for the sustainable production of light aromatics via the reductive depolymerization of lignin.