The positive impact of coworker social support on employee behaviour and well-being is well-described in the job demands–resources model. However, the specific mechanisms through which it operates have received scarce research attention. The current study investigated the distinct roles of relatedness need satisfaction (i.e. connectedness) and need frustration (i.e. isolation) to explain how available coworker social support relates to organizational citizenship behavior (OCB) and depersonalisation. We used a three-wave panel design (N = 1259/704/405 at Time 1/2/3) to test the indirect effects of social support on OCB via connectedness and on depersonalisation via isolation. Coworker social support at Time 1 predicted increases in connectedness and decreases in isolation from Time 1 to Time 2. Contrary to expectations, increases in connectedness predicted decreases in OCB, and decreases in isolation did not predict decreases in depersonalisation, from Time 2 to Time 3. Overall, our results highlight the importance of coworker social support to increase connectedness and decrease feelings of isolation in the workplace, which can ultimately affect interpersonal work outcomes.