Purpose Post-COVID fatigue significantly limits recovery and return-to-work in COVID-19 survivors. We aimed to assess the effects of physical exercising on post-COVID-19-symptoms, physical/mental capacities and workability within a workplace-health-promotion project in health-care personnel. Materials and methods Thirty-two HCWs were enrolled in two groups based on Post-COVID-Functional Scale (PCFS) scores: (1) severe (SSG, n = 11) and (2) mild (MSG, n = 21) symptoms. The participants underwent an eight week exercise intervention program consisting of two supervised resistance exercise sessions per week plus individual aerobic exercise recommendations. Primary outcome-parameter for physical fitness was VO(2)peak. Further, physical function (6MWT, 30 s sit-to-stand test (30secSTS)), mental health (anxiety (GAD-7), depression (PHQ-9), stress (PSS-10), fatigue (BFI), resilience (BRS)), cognitive capacity (MoCA) and workability (WAI) were assessed at baseline, after 4 weeks and after completion of exercise intervention. Results VO(2)peak improved significantly in the SSG by 2.4 ml/kg/min (95% CI [1.48; 3.01], adj.p < 0.001) and non-significantly in the MSG by 1.27 ml/kg/min (adj.p = 0.096). Both groups significantly improved their 30secSTS (p = 0.0236) and 6MWT (p = 0.0252) outcomes in both follow-ups (4 weeks and 8 weeks after inclusion). The SSG improved more than the MSG in VO(2)peak and 6MWT both after 4 and 8 weeks, respectively, although not statistically significant; findings were vice versa for the 30secSTS. 30secSTS outcomes correlated significantly with mental health outcomes and workability. Conclusions Post-COVID exercise intervention improved physical fitness, psychological outcomes and workability in HCWs. Cases with severe fatigue showed higher benefit levels compared to those with mild symptoms. The safe and highly feasible 30secSTS correlated well with physical and mental outcomes and better workability in COVID-19 survivors.