Ketanji Brown Jackson has been sworn in as the newest associate Supreme Court justice, becoming the first black woman to serve on the nation's highest court.
The appointment follows one of the most consequential Supreme Court terms in recent memory, with significant rulings on abortion and gun rights.
Ms Jackson, 51, will replace Justice Stephen Breyer, joining the court's three-member liberal minority.
She accepts "the solemn responsibility" of the role, she said in a statement.
The former public defender joins the court at a tumultuous period in its history. The nine-member court is currently split between six Republican-appointed justices and three picked by Democrats.
In recent weeks it delivered several blockbuster decisions - overturning the 50-year-old Roe v Wade decision on abortion, striking down a New York law restricting gun-carrying rights, and limiting the US Environmental Protection Agency's power to reduce greenhouse gas emissions.
The lifetime appointment will likely see Ms Jackson on the bench for decades but will not shift the current ideological balance of the court.
The addition of Ms Jackson to the court means that its liberal minority - with Justice Elena Kagan and Justice Sonia Sotomayor - will be made up entirely of women.
Mr Breyer congratulated his successor on Thursday, saying "her hard work, integrity, and intelligence have earned her a place on this court."
"I am glad for my fellow justices. They gain a colleague who is empathetic, thoughtful, and collegial," he said.
US President Joe Biden, a Democrat, announced her nomination in February. In April, three Republicans crossed the aisle to seal her appointment in the US Senate.
During her confirmation, Democrats touted Ms Jackson's experience working as a public defender. She will be the first Supreme Court justice since Thurgood Marshall - the first black man to appointed to the highest judicial body - to have career experience representing criminal defendants.
Ms Jackson, a Washington DC native, previously sat on the influential US court of Appeals for the DC circuit.
She has two degrees from Harvard University and once served as editor of the Harvard Law Review. She worked as a public defender in Washington before joining a private practice prior to her judicial appointments.