(CN) - Liberal Supreme Court Justice John Paul Stevens announced his retirement Friday, saying he will hang up his robe this summer after 34 years on the nation's highest court.
Stevens, who turns 90 this year, is one of the oldest and longest-serving justices in Supreme Court history. He joined the court in 1975, after being appointed by Republican President Gerald Ford.
He announced his retirement in a one-page letter to President Obama on Friday. His resignation gives Obama the chance to nominate his replacement and maintain the court's ideological balance.
The court is split 4-4, with moderate Justice Anthony Kennedy often casting the swing vote.
Democratic lawmakers praised Stevens' decision to retire while Obama is still in office, while Republicans have said they intend to make their voices heard during the confirmation process.
"As we await the president's nominee to replace Justice Stevens," Senate Republican leader Mitch McConnell said, "Americans can expect Senate Republicans to make a sustained and vigorous case for judicial restraint and the fundamental importance of an even-handed reading of the law."
The ACLU issued a statement thanking Stevens for his "distinguished service" and crediting him for upholding the rights of Guantanamo Bay detainees.
"The civil liberties legacy of Justice Stevens is deep and broad," ACLU Legal Director Steven Shapiro said. "He has promoted racial equality, supported gay rights and defended a woman's right to choose."
Shapiro added, "Justice Stevens has earned his retirement, but he will be sorely missed."
Read the Top 8
Sign up for the Top 8, a roundup of the day's top stories delivered directly to your inbox Monday through Friday.