Surface organic carbon content and soil moisture (SM) represent first-order controls on permafrost thaw and vulnerability, yet remain challenging to map accurately. Here we explored the links between surface organic soil properties and SM dynamics in the Alaska North Slope through data analysis and process-based modeling. Our analysis, based on in situ SM and brightness temperature data from the Soil Moisture Active Passive (SMAP) mission, indicated that the SM drydown process in Arctic tundra is closely related to surface soil organic carbon (SOC) properties. More rapid drydown was generally observed in areas with high SOC concentration (SOCC) or low bulk density. The drydown timescale derived from the SMAP polarization ratio (PR) was significantly correlated with SoilGrids surface (0–5 cm) SOCC data (R = −0.54 ∼ −0.68, p < 0.01) at regional scale. To understand the process, we used a coupled permafrost hydrology and microwave emission model to simulate changes in the L-band PR during the thaw season. The model accounts for the variations in organic soil hydraulic and dielectric properties with SOC content and decomposition state. Model sensitivity runs showed larger L-band PR decreases during the early thaw season in soils with higher SOCC consistent with the above analysis, whereby highly organic soils (SOCC > 34.8%) drain water more easily with a larger amount of water discharged or lost (through evapotranspiration) relative to soils with less carbon concentration (SOCC < 17.4%). Our findings indicate that satellite L-band observations are sensitive to tundra SM and carbon properties, and may provide critical constraints on predictions of Arctic permafrost thaw and vulnerability.