Continuous innovation has become a key to gaining a sustainable competitive advantage for organizations in the 21st century. By focusing on the underlying mechanisms (i.e., mindfulness and work engagement) by which it works, this study addresses the quality of leader–member relationships and their relevance for innovation in the workplace. Using a sample of 210 employees from 17 Spanish companies, a two-wave longitudinal design evaluated the mediational roles of mindfulness and engagement between leader–member exchange (LMX) quality and innovative work behavior (IWB) in an organizational context. Over the course of a year, two questionnaires were administered to measure LMX quality, mindfulness, engagement, and IWB. Results from structural equation modeling provided support for the hypothesized double-mediation model with a significant full double mediation. Findings suggested that mindfulness and engagement could be characteristic mechanisms of high-quality LMX that helps to facilitate innovation. Practical implications include its creative value in gaining a competitive edge over market competitors and helping organizations to find a sustainable source for their consistent growth through their human capital and innovative potential.