In this study, an attempt has been made to develop a model to predict the service life of geosynthetic-reinforced hot mix asphalt (HMA) overlay placed over distressed pavements based on fatigue behavior observed in beam and large-scale tests. A two-stage detailed experimental program was designed to understand the fatigue behavior and reinforcement effects of asphalt overlays reinforced with geosynthetic interlayers. During the first stage, small-scale beam flexural fatigue tests were conducted on the HMA overlays to understand the reflection cracking and deformation behaviors with the aid of digital image correlation (DIC) techniques. During the second stage, the fatigue behavior of overlays was evaluated under repeated load tests on large-scale pavement sections built over a weak subgrade in a large test tank. Two types of geosynthetic interlayers, namely, polyester grid coated with polymer modified binder (PE) and a glass-grid composite (GGC) with different tensile strength and strain characteristics, were employed. The beam flexural fatigue test results along with DIC data indicated that the geosynthetic-interlayers have effectively minimized the crack propagation into overlays even under unconfined conditions. Whereas, for the same permanent deformation, the large-scale test sections sustained a higher number of load repetitions, reaching 100-fold, because of the presence of a base course structural support. A simple model to estimate the service life of the geosynthetic asphalt overlays has been proposed based on the beam fatigue tests viz. normalized complex modulus × cycles and a corresponding number of load repetitions for a prescribed rutting. Overall, for a vertical deformation of about 7.5 mm, it is estimated that GGC and PE interlayers would give a service life of 4.1 and 2.9 years, respectively, in real field scenarios. © 2019 ASTM International. All rights reserved.