Barrett, 48, a favourite of religious conservatives, has been named by Trump to replace liberal Justice Ruth Bader Ginsburg, who died on September 18.

In 2017, Barrett was appointed by Trump to the Chicago-based 7th US Circuit Court of Appeals. She has proven reliably conservative in that post, voting in favour of one of Trump's hardline immigration policies and showing support for expansive gun rights. She also authored a ruling making it easier for college students accused of campus sexual assaults to sue their institutions.

"I love the United States and I love the United States Constitution," Barrett said at a ceremony on Saturday at the White House Rose Garden where Trump announced her nomination. "A judge must apply the law as written. Judges are not policy makers."

Abortion rights groups are worried that Barrett would vote as a justice to overturn the landmark 1973 Roe v. Wade Supreme Court decision that legalised abortion nationwide.

Although she has not yet ruled directly on abortion, Barrett twice signalled opposition to rulings that struck down Republican-backed Indiana abortion-related restrictions - one in 2018 requiring fetal remains to be buried or cremated after an abortion, the other in 2019 involving parental notification for minors seeking an abortion - voting to have those decisions reconsidered.

During Barrett's 2017 confirmation hearing, US Senator Dianne Feinstein said, "The dogma lives loudly within you." Barrett, a devout Roman Catholic, said her religious faith would not affect her decisions as a judge.

In June, Barrett dissented when a three-judge panel ruled in favour of a challenge to Trump's policy to deny legal permanent residency to certain immigrants deemed likely to require government assistance in the future. In January, the Supreme Court, powered by its conservative majority, allowed the policy to take effect.

She also made a ruling that revived a lawsuit by a male student who had been suspended from Purdue University after being accused of sexual assault. He accused the school of discriminating against him on the basis of his gender.

Barrett wrote that in the case it was plausible Purdue officials chose to believe the female accuser "because she is a woman" and to disbelieve the male student accused "because he is a man."

She indicated support for gun rights in a 2019 dissent when she objected to the court ruling that a nonviolent felon could be permanently prohibited from possessing a firearm.

Barrett, born in New Orleans, received her law degree from Notre Dame Law School, a Catholic institution in Indiana. She is married to Jesse Barrett, a lawyer in private practice and a former federal prosecutor in Indiana. They have seven children, two of whom were adopted from Haiti.

She previously served as a clerk for Supreme Court Justice Antonin Scalia, a stalwart conservative who died in 2016.

"I clerked for Justice Scalia more than 20 years ago, but the lessons I learned still resonate," Barrett said on Saturday. "His judicial philosophy is mine too."

She also praised Ginsburg and the liberal icon's long friendship with Scalia, despite profound legal differences between the two.

In a 1998 law journal article she and another author said that Catholic judges who are faithful to their church's teachings are morally precluded from enforcing the death penalty and should recuse themselves in certain cases.

Barrett and her family have been members of a Christian religious group called People of Praise, according to other members.

Craig Lent, the group's overall coordinator, said in 2018 that the organisation centres on close Christian bonds and looking out for one another. They also share a preference for charismatic worship, which can involve speaking in tongues.

Certain leadership positions are reserved for men and some women in leadership positions used to be called handmaids, but now are referred to as "women leaders," Lent said, to avoid the perception of servility.

Australian Associated Press