The landmark U.S. Supreme Court case that determined the constitutionality of segregation laws in 1954 was Brown v. Board of Education. This historic ruling declared that state-sanctioned segregation in public schools was unconstitutional, overturning the precedent established by Plessy v. Ferguson. The Court's unanimous decision emphasized that “separate but equal” educational facilities were inherently unequal, thus violating the Equal Protection Clause of the Fourteenth Amendment. This landmark case served as a catalyst for the civil rights movement, inspiring further legal challenges against segregation and promoting greater awareness of racial inequality.