In his majority opinion, Chief Justice Edward Douglass White held that Oklahoma's grandfather clause was "repugnant to the Fifteenth Amendment and therefore null and void".

[citation needed] The 15th Amendment to the Constitution of the United States provides the right to not be discriminated against while voting on the basis of race, color, or previous servitude.

[2] The grandfather clause in Guinn v. United States involved requirement that a citizen must pass a literacy test in order to register to vote.

It represented the second appearance before the Court of John W. Davis as United States Solicitor General and the first case in which the National Association for the Advancement of Colored People (NAACP) filed a brief.

The previous conditions of servitude based on the race or skin color of people rendered them incapable of gaining literacy or meeting the ambiguously formed loopholes within said clause.

[5] The Supreme Court handed down its decision in Guinn v. United States together with Myers v. Anderson, which concerned a grandfather clause in the Maryland constitution.

[6] In its decision published on June 21, 1915, the Court found "the grandfather clauses in the Maryland and Oklahoma constitutions to be repugnant to the Fifteenth Amendment and therefore null and void".

[7] In his majority opinion, Chief Justice Edward Douglass White held that the grandfather clause was clearly designed to interfere with the voting rights protections of the Fifteenth Amendment even though it was racially neutral on its face.

The Court ruled that the new statute still violated the Fifteenth Amendment because they were "operated unfairly against the very class on whose behalf the protection of the Constitution was here successfully invoked."