President Donald Trump has nominated Amy Coney Barrett, a favourite of social conservatives, to be the new Supreme Court justice.
Speaking by her side at the White House Rose Garden, Mr. Trump described her as a “woman of unparalleled achievement”.
If confirmed by senators, Judge Barrett will replace liberal Justice Ruth Bader Ginsburg who died recently, aged 87.
The nomination will spark a bitter confirmation fight in the Senate as November’s presidential election looms.
Announcing Judge Barrett as his nominee on Saturday, President Trump described her as a “stellar scholar and judge” with “unyielding loyalty to the constitution”.
Democratic presidential candidate Joe Biden urged the Senate not to “act on this vacancy until after the American people select their next president and the next Congress”.
“The United States Constitution was designed to give the voters one chance to have their voice heard on who serves on the Court. That moment is now and their voice should be heard,” he said.
If Judge Barrett is confirmed, conservative-leaning justices will hold a 6-3 majority on the Supreme Court for the foreseeable future.
The 48-year-old would be the third justice appointed by the current Republican president, after Neil Gorsuch in 2017 and Brett Kavanaugh in 2018.
The 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 for decades
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.
After graduating from Notre Dame University Law School in Indiana, she clerked for the late Justice Antonin Scalia. In 2017, she was nominated by Mr Trump to the Chicago-based 7th Circuit Court of Appeals.
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 1973 Supreme Court decision that legalised abortion nationwide.
LGBT groups have criticised her membership of a conservative Catholic group, People of Praise, whose network of schools have guidelines stating a belief that sexual relations should only happen between heterosexual married couples.
Judge Barrett has ruled in favour of President Trump’s hardline immigration policies and expressed views in favour of expansive gun rights.
Conservatives hope she will rule against the Affordable Care Act – a health insurance scheme introduced by President Trump’s Democratic predecessor Barack Obama.
Some 20 million Americans could lose their health coverage if the court overturns the legislation, also known as Obamacare.
Following Saturday’s announcement, Senate Democratic leader Chuck Schumer warned fellow senators that voting to confirm Judge Barrett could spell the end of Obamacare.
“A vote by any senator for Judge Amy Coney Barrett is a vote to strike down the Affordable Care Act and eliminate protections for millions of Americans.”
Judge Barrett on Saturday 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.