This study examines the critical role being played by the Government Accountability Office which functions as the national public auditor in ensuring the congressional control on public purse in USA. The author traces its origin, legal history, evolution and growth in the public finance management. The article describes the various models of audit that are accomplished by the Government Accountability Office which apprises the Congressmen and public concerning acts of commission and omission of the executive branch of the government pertaining to utilisation of public fund. The article analytically scrutinises the working and performance of the Government Accountability Office having mandate to evaluate government programmes and policies independently and without fear and favour from executive wing that makes it financial watchdog on financial affairs of the government and safeguards public interest.