Gideon's Promise Act - Amends the Omnibus Crime Control and Safe Streets Act of 1968 to require grant applicants under the Edward Byrne Memorial Justice Assistance Grant Program to include in grant applications a comprehensive state-wide plan for the improvement of the administration of the criminal justice system. Makes it unlawful for government entities or their agents to engage in a pattern or practice of conduct that deprives indigent defendants of their constitutional rights to assistance of counsel in criminal proceedings.