This study examined the relationship between financial management practices and the business sustainability of manufacturing firms in Nakawa Division, Kampala. Manufacturing firms operate in capital-intensive, competitive environments in which sound financial management is essential to long-term survival and growth. The study investigated how working capital management, financial planning, financial control, and investment decisions relate to business sustainability. A cross-sectional survey design with a mixed-methods approach was adopted, and data were collected from 165 respondents comprising owners, managers, and finance staff of manufacturing firms using structured questionnaires and interviews. Descriptive statistics, Pearson correlation, and structural (path) analysis were used. The results revealed a strong positive and significant relationship between financial management practices and business sustainability (r = 0.67, p < 0.01), with the practices jointly explaining 65.0% of the variance in sustainability (R² = 0.650). Working capital management (β = 0.32) and financial planning (β = 0.29) emerged as the strongest path predictors. The study concludes that sound financial management practices significantly enhance business sustainability and recommends strengthening working capital management, financial planning, and control.