The Main Recent Fault is a major right-lateral strike-slip fault in the western Zagros mountains of Iran. Previous studies have estimated a wide range of slip rates from both sparse GNSS (1–6 mm/yr) and geological/geomorphological (1.6–17 mm/yr) methods. None of these studies have estimated the depth to the top of the locked seismogenic zone. Characterizing this “locking depth” for the Main Recent Fault, and more accurately constraining its interseismic slip rate, are both critical for estimating the seismic hazard posed by the fault, as well as for understanding how oblique convergence is accommodated and partitioned across the Zagros. To address this important knowledge gap for the MRF, here we use 200 Sentinel-1 SAR images from the past 5 years, spanning two ascending and two descending tracks, to estimate the first InSAR-derived slip rate and locking depth for a 300 km long section of the fault. We utilise two established processing systems, LiCSAR and LiCSBAS, to produce interferograms and perform time series analysis, respectively. We constrain north-south motion using GNSS observations, decompose our InSAR line-of-sight velocities into fault-parallel and vertical motion, and fit 1-D screw dislocation models to three fault-perpendicular profiles of fault-parallel velocity, following a Bayesian approach to estimate the posterior probability distribution on the fault parameters. We estimate an interseismic slip velocity of $3.0\pm1.0$ mm/yr below a loosely constrained 18–30 km locking depth, the first such estimate for the fault, and discuss the challenges in constraining the locking depth for low magnitude interseismic signals.