Rack and pinion-based wave energy converter (WEC) is becoming a popular energy conversion device because of its simple structure and easy maintenance. The analysis of energy extraction under regular sinusoidal wave conditions was discussed in another study and a suboptimal energy extraction process was presented. However, analysis of such a device under irregular wave conditions is still needed. To fill this gap, this paper presents an analysis of a rack and pinion-based WEC under irregular wave conditions. A simulation model was developed to run under a realistic wave environment. The wave environment of six unique sea states from Newport, Oregon, was adopted. The control mechanism was tuned to accommodate the irregular wave conditions. Although the simulation results show different performance under regular and irregular wave conditions, significant amount of energy can still be extracted from irregular waves.