As the COVID-19 variant Omicron surge in Beijing, China, a better understanding of risk factors for adverse outcomes may improve clinical management in patients with haematological malignancies (HM) diagnosed with COVID-19. The study sample includes 412 cases, mainly represented by acute leukaemia, chronic myeloid leukaemia (CML), plasma cell disorders and lymphoma and chronic lymphocytic leukaemia. COVID-19 pneumonia was observed in 10.4% (43/412) of patients, and severe/critical illness was observed in 5.3% (22/412). Among the 86 cases with advanced malignancies, 17.6% (12/86) of patients developed severe/critical COVID-19, which was significantly higher than reported in patients with stable malignancies (9/326, 2.70%, p < 0.001). Similarly, the advanced malignancy cohort had a higher mortality rate (9/86, 10.5% vs. 0/326, 0%, p < 0.001) and a poor 30-day overall survival (OS) compared with the stable malignancy cohort (74.2% vs. 100.0%, p < 0.0001). Overall, nine patients (2.2%) died. The primary cause of death was progressive HM in four patients and a combination of both COVID-19 and HM in five patients. In the multivariable analysis, over 65 years of age, comorbidities and advanced malignancy were correlated with severe/critical COVID-19 in HM patients. This study sheds light on the poor outcomes among COVID-19 HM patients with the leading cause of advanced malignancy.