Fiber-reinforced polymer (FRP) composites are being utilized in an increasing number of applications in structural industries. Establishing values for longterm fatigue response is essential for widespread use of FRP composites. The variety of available fibers, matrix materials, and manufacturing processes makes the fatigue response difficult to predict without extensive empirical testing. A proposed fatigue life prediction model uses the internal strain energy release rate as the metric for predicting fatigue life from a minimum of data points. The objective of this research was to apply the above model to fatigue data for various composite coupons and components in order to evaluate its applicability in predicting fatigue life. The model was found to be able to regularly fit and predict fatigue data within 5% log error at both coupon and component levels. The effects of environmental conditions, including 12 MPa pressurized absorption and fatiguing in salt water and elevated temperatures, were also explored for a glass/vinyl ester FRP. The results of this research can be used to aid in the design of numerous structural FRP applications, such as windmill blades, bridge decks, or deep sea piping.