Progressive Justice Stephen Breyer - at 83 the oldest member of the US Supreme Court - will retire at the end of the court's current term that runs through the end of June, media reports say, giving US President Joe Biden the opportunity to appoint a successor who could serve for decades.
NBC News and CNN said on Wednesday that Breyer was expected to retire.
Breyer authored important rulings upholding abortion rights and healthcare access, helped advance LGBT rights and questioned the constitutionality of the death penalty but often found himself in dissent on a court that currently has a 6-3 conservative majority.
He was appointed to the Supreme Court by Democratic president Bill Clinton in 1994.
Only conservative Justice Clarence Thomas, one of two black men ever on the high court, has served longer among the current justices, joining it in 1991.
Biden during the 2020 presidential election campaign pledged to nominate a black woman to fill any Supreme Court vacancy, which would be a historic first.
Biden's fellow Democrats hold a razor-thin majority in the US Senate, which under the US constitution gets to confirm Supreme Court nominees.
Potential Biden nominees include Ketanji Brown Jackson, a former Breyer law clerk who was confirmed by the Senate last June to serve on an influential US appellate court, and Leondra Kruger, who serves on the California Supreme Court.
Thurgood Marshall is the only other black justice in US history, having served from 1967 to 1991.
A Biden appointee would not change the court's ideological balance but would enable him to refresh its progressive wing with a much younger jurist in the lifetime post.
Biden's Republican predecessor Donald Trump appointed three justices during his four years in office, all of whom were young enough to serve for decades.
The Senate, then under Republican control, confirmed Trump's appointment of conservative Justice Amy Coney Barrett in 2020 after the death of progressive Justice Ruth Bader Ginsburg.
After Biden defeated Trump in the 2020 election, some progressive activists urged Breyer to step aside while Democrats control the Senate, concerned that if he does not do so, Republicans could block confirmation of his successor in the chamber or a future Republican president could be able to name his replacement and tilt the court further to the conservatives.
The Senate is split 50-50, with Democrats in control because Vice President Kamala Harris can cast a tie-breaking vote.
Confirmation of a justice requires a simple majority vote rather than a previous 60-vote threshold under a change made by Senate Republicans in 2017 when they controlled the chamber and faced Democratic opposition to Trump's first Supreme Court nominee.
Australian Associated Press