The purpose of this study is to investigate the relationship among innovation, firm life-cycle extension and firm value in a structured way. We define the innovation as an improvement in productivity. This study classifies firms’ life-cycle into three stages (Growth, Maturity and Decline), and considers the life-cycle as extended when it moves from Decline to Growth or Maturity, shifts from Maturity to Growth, or maintains Growth for consecutive two years. The firm value is measured as the rate of return for stocks. We test whether the innovation is a major factor that extends firms’ life-cycle, and empirically analyze whether firms’ life-cycle extension has a moderation or mediation effect on the value relevance of the innovation. Our sample consists of manufacturing firms listed on the Korea Exchange from 2003 to 2017. The empirical results are summarized as follows. First, the innovation of a firm had a positive effect on the value of the firm. Second, we examined the relationship between innovation and firm life-cycle extension by measuring the innovation with parametric and non-parametric methods, and found that the measures of innovation had positive effects on firm life-cycle extension. Third, the value relevance of innovation was higher in firms with extended life-cycle, indicating that the firm life-cycle extension had a moderation effect on the relationship between innovation and firm value. Fourth, we found that the innovation had a positive effect on the firm value through the life-cycle extension, signifying that the improvement of firm life- cycle had a mediation effect on the value relevance of the innovation. This study presents empirical evidence that firm life-cycle extension has moderation and mediation effects on the value relevance of innovation. It implies that the innovation and life-cycle extension of a firm can be considered as a key factor in determining the value of the firm.