O’Melveny represented The American Bar Association in an amicus brief asking the US Supreme Court to protect the rights of Black voters in Alabama. The amicus brief urged the High Court to affirm a federal district court's ruling that Alabama’s 2021 congressional redistricting plan violated the federal Voting Rights Act by diluting the power of Black voters.

“The Gingles interpretation has been settled law for 36 years without congressional revision,” the ABA brief said, citing the Supreme Court’s 1986 decision in Thornburg v. Gingles. “And throughout multiple redistricting cycles, litigants and governments have relied on Gingles as the test to balance governments’ redistricting prerogatives and minorities voting rights.”

The Supreme Court agreed in a June 2023 decision, ruling that the Alabama Legislature’s redistricting ran afoul of the Voting Rights Act by concentrating a large number of Black voters in a single congressional district and reducing their influence in other six districts. The Supreme Court ordered the Legislature to redraw the map.