This article addresses the impact of temporary employment on workers’ social identification, work motivation, and reactions to injustice at the workplace. More precisely, we examined whether organisational identification mediates the effect temporary work (compared to permanent employment) on work motivation, and reactions to injustice. We also examined whether autonomy in contract-choice and compensating features of job contracts (employment duration, qualification matching, and negotiated wages) have positive effects on the organisational and ingroup identifications of temporary workers. Finally, we examined whether ingroup identification of temporary workers act as a mediator and moderates the effect of organisational identification. Results from a survey comparing agency workers with fixed-term and permanent employees mainly from the industry sector first reveal that organisational identification mediates the negative effect of temporary work on work motivation and its positive association with self-centred reactions to injustice. Nevertheless, cluster analysis revealed the existence of three subgroups of agency workers, a minority of them—autonomous and compensated—having similarly high levels of identification and motivation than permanent employees. Additionally, autonomous and compensated workers identify more with their ingroup than low-autonomy and low-compensations workers, ingroup identification explaining their difference in terms of work motivation. Furthermore, ingroup identification of agency workers interact with organisational identification to determine their reactions to injustice. Implications, limitations, and research perspectives deriving from this study are discussed.