Background: Early diagnosis of tuberculosis (TB) is important to reduce transmission, morbidity and mortality in people living with HIV (PLWH). Methods: PLWH with a diagnosis of TB were enrolled from HIV and TB clinics in Eastern Europe and followed until 24 months. Delayed diagnosis was defined as duration of TB symptoms (cough, weight-loss or fever) for ≥ 1 month before TB diagnosis. Risk factors for delayed TB diagnosis were assessed using multivariable logistic regression. The effect of delayed diagnosis on mortality was assessed using Kaplan–Meier estimates and Cox models. Findings: 480/740 patients (64.9%; 95% CI 61.3–68.3%) experienced a delayed diagnosis. Age ≥ 50 years (vs. < 50 years, aOR = 2.51; 1.18–5.32; p = 0.016), injecting drug use (IDU) (vs. non-IDU aOR = 1.66; 1.21–2.29; p = 0.002), being ART naïve (aOR = 1.77; 1.24–2.54; p = 0.002), disseminated TB (vs. pulmonary TB, aOR = 1.56, 1.10–2.19, p = 0.012), and presenting with weight loss (vs. no weight loss, aOR = 1.63; 1.18–2.24; p = 0.003) were associated with delayed diagnosis. PLWH with a delayed diagnosis were at 36% increased risk of death (hazard ratio = 1.36; 1.04–1.77; p = 0.023, adjusted hazard ratio 1.27; 0.95–1.70; p = 0.103). Conclusion: Nearly two thirds of PLWH with TB in Eastern Europe had a delayed TB diagnosis, in particular those of older age, people who inject drugs, ART naïve, with disseminated disease, and presenting with weight loss. Patients with delayed TB diagnosis were subsequently at higher risk of death in unadjusted analysis. There is a need for optimisation of the current TB diagnostic cascade and HIV care in PLWH in Eastern Europe.