Donald Trump has announced his pick for the Supreme Court, nominating conservative Judge Amy Coney Barrett, a Catholic and mother of seven.

Mr Trump hopes to galvanise his supporters with the decision which caps a dramatic reshaping of the federal judiciary that will resonate for a generation.

Shockwaves of the appointment immediately resounded through Washington, with Democrats saying Ms Barrett’s appointment could spell the end for abortion rights and access to health care.

“Justice Ginsburg must be turning over in her grave up in heaven,” top Senate Democrat Chuck Schumer said, “to see that the person they chose seems to be intent on undoing all the things that Ginsburg did.”

The President made the announcement on Sunday morning Australian time, praising the credentials and “towering intellect” of Barrett who is also the first mother of school-age children on the court.

“Today, it is my honour to nominate one of our nation’s most brilliant and gifted legal minds to the Supreme Court,” he said in the Rose Garden at the White House.

“She is a woman of unparalleled achievement, towering intellect, sterling credentials and unyielding loyalty to Constitution – Judge Amy Coney Barrett.”.

Mr Trump said Barrett’s record was “beyond reproach” however her nomination is expected to set off a battle between Republications and Democrats ahead of the US presidential election in November.

The appointment would give conservatives a 6-3 majority on America’s highest court.

Ms Barrett, 48, could be on the bench for the court’s November 10 oral arguments in a case in which Trump and fellow Republicans are seeking to invalidate the 2010 ‘Obamacare’ law, formally called the Affordable Care Act.

The nominee said she respected the President’s “momentous decision” and pledged to work to the best of her ability if her appointment was confirmed by the senate.

She would be the youngest justice, and her tenure could last for decades.

‘I am truly humbled by the prospect of serving on the Supreme Court,” she said.

US President Donald Trump announces his US Supreme Court nominee, Judge Amy Coney Barrett (R), in the Rose Garden of the White House. Photo: AAP

Barrett has been hailed by religious conservatives and others on the right as an ideological heir to conservative icon Antonin Scalia, the late Supreme Court justice for whom she clerked.

But liberals say her legal views are too heavily influenced by her religious beliefs and fear her ascent to the nation’s highest court could lead to a scaling back of hard-fought abortion rights.

“Donald Trump and Mitch McConnell have made it clear they will pull out all the stops to jam through another right-wing Supreme Court nominee – even if that means breaking their own rule pertaining to election-year appointments,” Democratic Senator Ron Wyden said.

Barrett has been a judge since 2017, when Mr Trump nominated her to the Chicago-based 7th US Circuit Court of Appeals.

Mr Trump’s selection follows the death of Ruth Bader Ginsburg, a feminist and liberal icon who was a strong defender of abortion rights.

Ginsburg, 87, died last weekend after a battle with cancer.

Democrat presidential candidate Joe Biden immediately responded to Supreme Court nomination, urging the senate not to act on it.

“The American people know the U.S. Supreme Court decisions affect their everyday lives,” he said in a statement.

“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.”

Earlier

According to reports in The New York Times and CNN, citing anonymous sources, Mr Trump intends to nominate Coney Barrett, a conservative and devout Catholic.

Coney Barrett is a Republican favourite because of her previous stances on abortion rights, guns rights and immigration.

“They say the biggest thing you can do (as president) is the appointment of judges, but especially the appointment of Supreme Court justices,” Mr Trump said earlier at a campaign rally in Virginia.

“That’s the single biggest thing a president can do, because it sets the tone of the country for 40 years, 50 years.”

Speaking to pool reporters while travelling from Florida, Mr Trump said he has picked a “very highly thought of person”.

“You will find out tomorrow,” he said, adding that it “could be any one of them”.

Conservative judge Amy Coney Barrett is tipped to the president’s top pick for the Supreme Court. Photo: AAP

The President has pledged to nominate a woman, with Coney Barrett at the top of the list, which also includes Barbara Lagoa, a federal judge, who comes from an Hispanic background.

Democrats accuse Republicans of seeking a Supreme Court judge who will peel away abortion rights in the country, along with invalidating the healthcare plan passed by former President Barack Obama.

Mr Trump has already appointed two Supreme Court judges in less than four years, both seen as conservatives.

Judges get lifetime appointments to the nine-member top court.