Anionic redox activity has recently been shown to be an important process that governs the electrochemical behavior of lithium-rich layered oxide electrodes. In 3d transition metal (TM) systems, it is typically believed that during the first charge this redox activity occurs via reversible depopulation of localized O2p electronic states. However, the electrochemistry of lithium-rich layered oxides with 3d TMs changes drastically after the first charge, suggesting that the redox mechanisms likely change. In this work, we investigate the nature of this change and reveal the crucial role of oxygen redox in mediating the unusual electrochemistry in these materials. By coupling a variety of structural probes with Scanning Transmission X-ray Microscopy (STXM) throughout the entire cycle life of a Li- and Mn- rich Ni/Mn/Co layered oxide (LMR-NMC), we correlate spatially localized transmission X-ray Absorption Spectra (XAS) at the TM L edges and O K edge with the evolving LMR-NMC atomic structure. Through our results we develop a unifying picture of how the structure-redox processes in LMR-NMC evolve as the material degrades, considering anion redox, transition metal migration, oxygen evolution, and vacancy formation. Specifically, we find that anion redox plays a crucial role in both the charge/discharge hysteresis during all cycles as well as the fading voltage over extended cycling. Our results paint a holistic picture of the electrochemical mechanism of LMR-NMC, linking understanding of the structural evolution, redox mechanisms, and electrochemical behaviors.