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This thesis highlights the versatility of nickel as a transition metal that enables the activation of relatively inert chemical bonds and offers lower energy pathways to challenging bond formations. In this work, reaction development and mechanistic inquiry inform one another, enhancing our understanding of nickel catalysis.Despite major advancements in C-heteroatom cross-coupling enabled by Ni-photoredox catalysis, the mechanisms of this form of catalysis are not well understood and are highly debated. Although mild Ni-photoredox C-N cross-coupling had been reported for strong N-nucleophiles like alkylamines, such a reaction involving weak N-nucleophiles such as amides had not been reported. This work describes the development of an unprecedented Ni-photoredox-catalyzed amide arylation reaction that proceeds under mild conditions. These mild conditions enable access to a broad scope including base-sensitive functional groups and excellent preservation of epimerizable stereocenters.We hypothesized that this amide arylation reaction might proceed via an alternative mechanism to the self-sustaining Ni(I/III) cycle that is usually reported for Ni-photoredox C-N coupling. This is because our reaction utilizes a redox-inactive base and weak N-nucleophiles, whereas the prior published methods in this arena couple strong N-nucleophiles and require redox-active bases as electron shuttles. A combined approach involving stoichiometric experiments with synthesized Ni complexes and the measurement of kinetic profiles of the catalytic reaction led us to propose an unusual Ni(0/II/III) cycle, which has a profound consequence for the rate-limiting step and the overall reaction kinetics. Kinetic studies probing the effect of nickel precatalysts of variousviioxidation states revealed a marked induction period with Ni(II) precatalysts, providing insight into the photochemical process that generates the active Ni(0) species.This thesis will also discuss the optimization and mechanistic investigation of a dual nickel/Lewis acid catalyst system that is capable of breaking carbon-carbon bonds in cyclopropanes and benzonitriles in a catalytic cyanide transfer reaction. The mechanism by which the catalyst is able to activate nitriles as relatively nontoxic cyanide surrogates is explored. Extensive efforts towards the design of an optimal ligand for regioselective ring-opening cyanation utilizing the modular phosphinooxazoline (PHOX) platform are described herein. Ligand optimization, mechanistic investigation, and determination of scope for this chemistry are ongoing.