The shallow segment of subduction plate boundary faults (<10 km) hosts diverse slip modes including low-frequency earthquakes and slow slip. These slip behaviors are thought to be controlled by the mechanical properties of rocks and sediment present along the subduction interface and their thermal and hydrologic environment. The roles of fluids have particularly gained a lot of attention over the past 20 years as numerous geophysical studies have shown a correlation between slow earthquakes and evidence of high pore fluid pressure along subduction thrusts. However, the mechanics of slip in shallow, fluid-rich subduction shear zones are not well constrained. We present three studies addressing different roles that fluids play in affecting the strength and slip behavior of shallow subduction thrust faults. Using deformation experiments, we first quantify the frictional constitutive behavior of chlorite, which is a ubiquitous and important hydrous mineral in subduction zones. Rate-stepping shear experiments were performed under shallow hydrothermal conditions with varying temperature, pore fluid pressure, and slip rates from 10-9 to 10-5 m/s, representing slow slip speeds and the faster velocities previously used to study chlorite deformation. Our results show that chlorite strengthens with increasing temperature and transitions from stable to unstable frictional behavior with decreasing slip rate, indicating that slow slip can nucleate in chlorite-rich fault zones. Based on microstructural observations and micromechanical analyses, we interpret this transition is controlled by a competition between rate-strengthening mineral deformation at grain contacts, which promotes stable sliding, and the time-dependent strength of water films between grains, which promotes rate-weakening (unstable) behavior. Along shallow subduction faults, pore fluid pressure can become elevated due to disequilibrium compaction of sediments or fluid release due to dehydration reactions like the smectite to illite transition. In our second study, we investigate whether the source of fluid overpressure places a role on the mechanics of shallow subduction fault slip. We conducted hydrothermal shear experiments on chlorite gouge and natural cataclasite from the Rodeo Cove thrust (RCT) in California along stress paths that simulate disequilibrium compaction and dehydration reactions. Our results show that the effects of pore fluid pressurization on fault strength can generally be described using the critical state soil mechanics (CSSM) framework. The effects of path are more pronounced and persist to greater displacements in chlorite fault rock than in cataclasite, which we attribute to differences in microstructure. Because of the effects on microstructure, effective stress path also imparts a much more significant control on the stability of chlorite-rich faults, which is not predicted by CSSM. Our second study thus provides constraints on how both the source of pore fluids and fault rock composition should be considered in models of shallow subduction faulting. In our third study, we characterize the effects that fluid-mediated reactions have on the rheology of oceanic crust in a shallow subduction thrust environment (8-10 km). To do so, we present a geochemical and microstructural study of metabasaltic fault rock from the Rodeo Cove thrust zone. At the RCT, deformation is distributed along a dense network of reddish and greenish foliated cataclasites, which surround blocks of altered basalt that contain abundant calcite veins and cement. Our study indicates that faulting and cataclasis of the altered basalt followed by seawater-mediated K-metasomatism promoted extensive mineralization of celadonite within the RCT, which influenced its overall strength and deformation style. Transitions from spilitization to K-metasomatism of oceanic crust may therefore play an important role in the mechanics of shallow subduction fault slip, especially along active sediment-poor margins.