Background/Objectives: The clinical impact of neutrophil-to-lymphocyte ratio (NLR) and right ventricular (RV) dysfunction on clinical outcomes in COVID-19 remains understudied in the Indonesian population. This study aims to investigate their prognostic value in hospitalized Indonesian adults with COVID-19. Methods: A retrospective cohort study was conducted at a COVID-19 referral hospital in Indonesia. We included all consecutive adults hospitalized between April 2020 and April 2021 who underwent transthoracic echocardiography (TTE) during admission. Clinical information was extracted from electronic medical records. TTE variables were defined according to the American Society of Echocardiography criteria. Statistical analyses were performed using SPSS. Ethical approval was obtained from the Institutional Review Board of Universitas Indonesia (#2022-01-135). Results: A total of 488 patients were included in this study—29 with and 459 without RV dysfunction. The mean age of the population was 54.8, with 42% being female. An NLR >4.793 was considered elevated. Elevated NLR was independently associated with RV dysfunction (OR: 3.38, p = 0.02). Older age (HR: 1.02, p = 0.01), obesity (HR: 1.85, p < 0.01), chronic kidney disease (HR: 1.69, p = 0.01), high NLR (HR: 2.75, p < 0.001), and RV dysfunction (HR: 2.07, p = 0.02) independently increased the risk of 30-day mortality by multivariate Cox regression analysis. Conclusions: In adult Indonesian patients hospitalized with COVID-19, an elevated NLR was associated with RV dysfunction, and both of these parameters increased the risk of 30-day mortality. This retrospective cohort study highlights the prognostic importance of NLR and RV dysfunction in hospitalized COVID-19 patients, providing physicians with tools to identify high-risk patients. © 2025 by the authors.