US President Donald Trump has nominated Amy Coney Barrett, a favourite of social conservatives, to be the new Supreme Court justice.
Speaking at the White House Rose Garden, Mr Trump described her as a "woman of unparalleled achievement".
Judge Barrett would replace liberal Justice Ruth Bader Ginsburg, who died of cancer on 18 September.
Her nomination will spark a bitter Senate fight to get her confirmed as November's presidential election looms.
Supreme Court justices are nominated by the US president, but must be approved by the Senate.
Mr Trump said Judge Barrett was a "stellar scholar and judge" with "unyielding loyalty to the constitution".
If Judge Barrett is confirmed, conservative-leaning justices will hold a 6-3 majority on the US's highest court for the foreseeable future.
The 48-year-old would be the third justice appointed by this Republican president, after Neil Gorsuch in 2017 and Brett Kavanaugh in 2018.
The Supreme Court's nine justices serve lifetime appointments, and their rulings can shape public policy on everything from gun and voting rights to abortion and campaign finance long after the presidents who appoint them leave office.
In recent years, the court has expanded gay marriage to all 50 states, allowed for Mr Trump's travel ban on mainly Muslim countries to be put in place, and delayed a US plan to cut carbon emissions.
Tricky position for Democrats
Amy Coney Barrett has been on Donald Trump's shortlist for Supreme Court vacancies for some time, but the word was that she would be the most appropriate replacement for Ruth Bader Ginsburg.
As of last week, that was no longer a hypothetical scenario.
Even before Mr Trump reportedly settled on Judge Barrett as his pick, conservatives were rallying around the nominee, whoever it might be. And if they stick together, as all but two seem to be doing, her confirmation appears assured – whether it is before November's election or in a "lame duck" Senate session afterward.
The choice of Judge Barrett puts Democrats in a tricky position. They have to find a way of undermining support for the nominee without seeming to attack her Catholic faith or personal background – moves that could risk turning off some voters in November. They will seek to delay the proceedings as best they can, while keeping their focus on issues like healthcare and abortion, which could be at the centre of future legal battles with Justice Barrett on a conservative-dominated court.
Then they have to hope Judge Barrett, or the Republicans, make some kind of critical error. It is a tall order, but for the moment it is the only play they have.
Who is Amy Coney Barrett?
She is described as a devout Catholic who, according to a 2013 magazine article, said that "life begins at conception". This makes her a favourite among religious conservatives keen to overturn the landmark 1973 Supreme Court decision that legalised abortion nationwide.
Her links to a particularly conservative Christian faith group, People of Praise, have been much discussed in the US press. LGBT groups have pointed out that the group's network of schools have guidelines stating a belief that sexual relations should only happen between heterosexual married couples.
One such group, Human Rights Campaign, has voiced strong opposition to Judge Barrett's confirmation, declaring her an "absolute threat to LGBTQ rights".
Judge Barrett has also ruled in favour of President Trump's hardline immigration policies and expressed views in favour of expansive gun rights.
Conservatives hope she will help to invalidate Obamacare, the health insurance programme that was introduced by President Trump's democratic predecessor, Barack Obama.
Some 20 million Americans could lose their health coverage if the court overturns the Affordable Care Act (ACA).
Democrats have rallied support over this issue, but it is thought unlikely that the Supreme Court will rule on the ACA before the 3 November election.
Following her nomination on Saturday, Judge Barrett said her rulings as a Supreme Court justice would be based only on the law.
"Judges are not policymakers, and they must be resolute in setting aside any policy view they might hold," she said.
Judge Barrett was one of the names the president considered to replace Justice Anthony Kennedy in 2017.
After graduating from Notre Dame University Law School in Indiana, she clerked for the late Justice Antonin Scalia, who died in 2016. She served as a legal scholar at Notre Dame for around 15 years.
Battle over Supreme Court
Will Judge Barrett be confirmed?
The White House has begun contacting Republican Senate offices to schedule meetings with the nominee next week, two sources familiar with the planning told CBS.
The courtesy calls are expected to start on Wednesday.Read More – Source