This study examined the effect of cost management on the financial performance of telecommunication companies in Nigeria. The research specifically investigated budgetary control and cost reduction strategies as dimensions of cost management, and profitability and liquidity as measures of financial performance. The study adopted an explanatory research design, combining primary data from 120 managerial and financial staff across leading Nigerian telecommunication firms with secondary data from financial statements spanning 2018–2023. Data were analyzed using descriptive statistics, multiple regression, and ANOVA tests. The findings revealed that both budgetary control and cost reduction strategies have a significant positive effect on profitability and liquidity. Budgetary control was found to have slightly more influence, highlighting the importance of structured budgeting, monitoring, and variance analysis. The regression models indicated that cost management practices explain 74.3% of the variation in profitability and 64.6% of the variation in liquidity, demonstrating a strong relationship between effective cost management and financial performance. The study concluded that cost management is a critical driver of financial sustainability in Nigerian telecommunication companies. It is recommended that firms strengthen budgetary control systems, implement strategic cost reduction initiatives, integrate cost management into strategic planning, and leverage technology to enhance financial outcomes.