This study examined systemic corruption, abuse of political power, fiscal indiscipline, weak institutional accountability, and democratic governance challenges within Nigeria’s democratic polity. The study was undertaken to investigate the extent to which corruption, excessive public borrowing, political interference, and weak governance institutions have affected democratic accountability, socio-economic development, and public confidence in governance across Nigeria. The major objective of the study was to critically evaluate the relationship between corruption and governance failures with particular emphasis on fiscal transparency, institutional efficiency, democratic stability, and sustainable national development. The study adopted a mixed-method research approach involving both qualitative and quantitative research designs, while descriptive survey and exploratory research methods were employed to obtain empirical data across the six geopolitical zones of Nigeria. The population of the study comprised approximately 155 million Nigerians, including government officials, politicians, legislators, youth and women organisations, non-governmental organisations, religious leaders, journalists, media practitioners, heads of tertiary institutions, ministries, departments, agencies, commissions, boards, parastatals, and other governance stakeholders. The Yaro Yamane (1967) mathematical sampling technique was applied in determining a scientifically representative sample size of 400 respondents for the study. Primary data were obtained through structured questionnaires, oral interviews, observational procedures, and documentary assessments, while secondary data were sourced from peer-reviewed journals, government publications, textbooks, reputable scholarly online publications, policy documents, and institutional reports. Institutional Theory, Elite Theory, and Structural Functionalism Theory were adopted as analytical frameworks for explaining governance failures, institutional weaknesses, political power concentration, and democratic accountability challenges within Nigeria’s democratic administration. Data obtained during the study were analysed using percentages, frequency distributions, correlation analysis, regression analysis, and thematic content analysis, while the Statistical Package for the Social Sciences IBM SPSS Statistics and Microsoft Excel were utilised for coding, tabulation, processing, interpretation, and graphical presentation of data. The findings revealed that systemic corruption, political interference, excessive public borrowing, electoral irregularities, selective anti-corruption enforcement, and weak judicial independence have significantly undermined democratic governance, economic stability, institutional credibility, and sustainable national development in Nigeria. The study therefore recommended stronger institutional independence, transparent fiscal governance, electoral reforms, ethical leadership orientation, youth empowerment programmes, judicial autonomy, and strengthened accountability mechanisms as essential prerequisites for sustainable democratic governance and national development in Nigeria.