By applying the job demand-resources and conservative of resources theories, this three-wave study (with eight-month intervals) explains the development of psychological hardiness in work environment, over time. Specifically, we invested the cross-lagged relationship between work engagement and hardiness, as well as the cross-lagged mediational effects of job crafting (related to seeking structural/social resources and challenges). The study was conducted among 839 human services professionals, belonging to three occupational sectors: health care, education and customer service. The hypothesis was verified by using of structural equation modelling. The obtained results found that: (1) work engagement play a driving role in the development of hardiness and job crafting over time; (2) only crafting related to seeking challenging demands mediates the cross-lagged effect of engagement on hardiness; (3) work engagement and hardiness can positively reinforce each other over time. No significant effects were observed for the links related to hardiness – job crafting and job crafting – engagement connections. A better insights into the hardiness development process may be interested for managers, HR specialists and team leaders. Based on the obtained results, they may project occupational health interventions intended to raise positive emotional states at work and encourage the increase of challenges.