The current diary study among 50 Spanish dual-earner couples examines whether engagement at work has an impact on own and partners’ well-being. Based on the Spillover–Crossover model, we hypothesized that individuals’ work engagement would spill over to the home domain, increasing their happiness level at the end of the day. Moreover, we predicted a crossover of happiness between the members of the couple. Participants filled in a diary booklet during five consecutive working days (N = 100 participants and N = 500 occasions). The results of multilevel analyses showed that daily work engagement has a direct effect on daily happiness. We also found that employees’ daily work engagement influenced partner’s daily happiness through employees’ daily happiness. Finally, results showed a clear bidirectional crossover of daily happiness between both members of the couple. These findings indicate that the positive effects of work engagement go beyond the work setting and beyond the employee.