Passed by Congress on March 3, 1869, and ratified in 1870, the Fifteenth Amendment was the last of the three Reconstruction Amendments. Though the language of the Fifteenth Amendment prohibits all race-based discrimination in qualifications for voting, the framers were primarily concerned with the enfranchisement of African-Americans. As early as 1866, many of the Republicans were convinced of the need for a constitutional amendment that would require the states to allow African-Americans to vote. Indeed, at one point the Joint Committee on Reconstruction voted to report a version of the Fourteenth Amendment that explicitly embraced the principle of race-blind suffrage. However, many Northerners continued to oppose black suffrage in principle, and fears of a political backlash led the committee to abandon the issue before the proposed amendment came to the floor. By 1869, the situation had changed. Although the outcome of referenda on black suffrage in the North continued to reflect the opposition of critical swing voters, other factors persuaded mainstream Republicans in Congress of the need for a federal constitutional amendment to deal with the issue.

Republicans had a variety of different reasons for supporting such an amendment. In the Reconstruction Act of 1867, Congress had forced black suffrage on the ex-Confederate states by statute, and Republicans faced the charge that they were hypocritical in not imposing the same requirement on Northern states. Some also believed that if blacks were enfranchised in the states that had remained in the Union, they would provide critical support for Republican candidates in those states. Still others argued that, even in the South, black suffrage would be insecure without a constitutional amendment and that the governments of the ex-Confederate states could not be returned to local control until the political power of the freed slaves was guaranteed.

By 1869, these considerations, combined with the conviction that allowing blacks to vote was right in itself, convinced virtually all mainstream congressional Republicans that a constitutional amendment was desirable. Republicans were, nevertheless, deeply divided over the question of what precise language should be adopted. Initially, the House of Representatives adopted a proposal quite similar to the current Fifteenth Amendment. However, a number of prominent Republicans complained that this narrow language would allow states intentionally to disfranchise most African-Americans by adopting qualifications that, although neutral on their face, would in practice be impossible for most freed slaves to satisfy. Responding to these and other concerns, the Senate proposed to eliminate not only discrimination on the basis of race, color, and previous condition of servitude but also discrimination on the basis of nativity, property, education, or creed in both the right to vote and the right to hold elective office. In ordinary circumstances, one might have expected a conference committee to have been convened at this point. However, in the complex parliamentary maneuvering that followed, the Senate did not vote to enter into conference; instead, the entire drafting process began again in both houses. The House then produced a draft that tracked the original Senate version, except that it deleted the reference to discrimination on the basis of education. The Senate, by contrast, now passed a simple prohibition on racial discrimination with respect to the rights to vote and hold office. A conference committee was convened, and it produced the current language of the Fifteenth Amendment, which embraced only the prohibition on racial discrimination in voting, omitting any reference to the right to hold office.

In short, because of the difficulty of agreeing to the precise language, the framers adopted a simple prohibition on discrimination on the basis of race, color, and previous condition of servitude even though there was a risk that a court could interpret the language narrowly and thereby allow deliberate evasion by facially neutral statutes. At first, the Supreme Court did exactly that and refused to inquire into the motives of those who adopted facially neutral statutes, such as literacy tests. Williams v. Mississippi (1898). Subsequently, the Court took a slightly broader view and voided a grandfather clause, the effect of which was to allow illiterate whites to vote, on the ground that it could have no conceivable purpose other than racial discrimination. Guinn v. United States (1915). More recently, the Court has invoked both the Fourteenth and Fifteenth Amendments to invalidate facially neutral restrictions on voting rights where the legislative history reveals an intention to exclude or hinder African-Americans. Rogers v. Lodge (1982), Hunter v. Underwood (1985). The Court also invoked the amendments in cases where there was evident racial gerrymandering designed to disenfranchise blacks. Gomillion v. Lightfoot (1960). On the other hand, the Court has held that race may be considered in the redistricting process only so long as racial considerations do not predominate and there is no effort to dilute the voting strength of minorities. Bush v. Vera (1996).

Similarly, the Court adopted variable views on the sweep of congressional authority under the enforcement clause. One critical issue was whether the amendment armed Congress with the power to regulate purely private action. Many of the congressional Republicans, who were responsible for passing the Fifteenth Amendment, apparently believed they had such authority: a section in a statute passed in 1870 made private, racially motivated interference with voting a federal crime. Nonetheless, although Ex parte Yarbrough (1884) suggested that this statute was constitutional, in 1903 the Supreme Court reversed course and held that the Fifteenth Amendment did not allow Congress to regulate purely private activity. James v. Bowman (1903). This basic principle was maintained until at least 1941, United States v. Classic, although the Court preferred to take the route of expansively defining nongovernmental activity as state action for purposes of the Fifteenth Amendment, applied particularly to the institution of the white primary. Smith v. Allwright (1944), Terry v. Adams (1953).

Although the legislative history of the Fifteenth Amendment provides little direct guidance on the precise scope of the enforcement authority under Section 2, recent decisions have upheld the constitutionality of sweeping remedial measures adopted to combat government-imposed racial discrimination. For example, when Congress had evidence of widespread racial discrimination in state elections, the Court allowed Congress to place the entire state and local electoral apparatus under federal supervision and to forbid the adoption of measures that had even the effect of diluting the voting power of racial minorities. Thornburg v. Gingles (1986). The Court, asserting that enforcement power had the same breadth as a necessary and proper clause, has also upheld the power of Congress to forbid literacy tests. South Carolina v. Katzenbach (1966). However in 2009, a majority of the justices suggested that Congress could no longer subject state electoral processes to such intrusive federal supervision unless there was evidence of continuing wide-spread racial discrimination in those practices. Northwest Austin Municipal Utility District No. 1 v. Holder (2009). Morover, in Shelby County v. Holder (2013), the Court struck down Section 4 of the Voting Rights Act of 1965, which had required certain states and voting districts to obtain preclearance from the U.S. Department of Justice before putting changes in voting procedures or districting into effect. Chief Justice John Roberts opined that the federal government may not discriminate against the equal sovereignty of the states absent evidence of a violation of federal law. He concluded that the formula that had been established in 1965 to determine which states should be subject to preclearance was outdated and could no longer justify the imposition of that burden on the designated state in the year 2013.