Key keywords: Supreme Court, mail-in ballot grace period, post-Election Day ballot counting, 2024 US general election, voting rights, election integrity, absentee ballot rules, swing state election policies In a 5-4 ruling issued on October 16, 2024, the U.S. Supreme Court upheld state-level grace period policies for counting mail-in ballots, rejecting a legal challenge that sought to invalidate Pennsylvania’s 3-day post-Election Day counting window for ballots postmarked on or before Election Day. The lawsuit, filed by Pennsylvania Republican Party officials and conservative election groups, argued that the grace period violated the U.S. Constitution’s Elections Clause, which grants state legislatures exclusive authority to set election timing and eligibility rules. The ruling marks a landmark decision that clarifies legal standing for similar grace period policies currently in place across 12 U.S. states, including key 2024 swing states Michigan, Nevada, Wisconsin, and Arizona. Prior to the ruling, election administrators across these states had expressed concern that ongoing legal challenges to their counting rules would lead to mass disqualification of valid ballots and extended post-election vote-counting disputes in the tight presidential race between incumbent Kamala Harris and former president Donald Trump. Nonpartisan election research group Voting Rights Lab estimates that over 140,000 validly postmarked mail-in ballots were disqualified across the U.S. during the 2020 and 2022 general elections solely for arriving after Election Day, even when postal delays outside of voters’ control caused the late delivery. The Supreme Court’s decision notes that states have the right to adopt reasonable administrative accommodations to ensure eligible voters are not disenfranchised by factors outside their control, as long as the policies are formally authorized by state law or state constitutional provisions. Responses to the ruling have split largely along partisan lines. The U.S. Department of Justice’s Voting Rights Section called the decision “a critical win for eligible voters across the country,” while the Republican National Committee released a statement saying it would pursue state-level legislative efforts to roll back grace period policies in all states where Republicans control legislative chambers. Election administration experts note that the ruling will significantly reduce the risk of post-election litigation over ballot counting in swing states, which many had warned could delay the announcement of 2024 election results by weeks or even months.