President Donald Trump has chosen Neil Gorsuch, 49, as his much anticipated nomination for the Supreme Court.

The youngest nominee for more than a decade, Gorsuch could face a contentious battle to be approved by Senate before he can be appointed to the vacant spot on the nine-seat panel. The scholarly conservative has a track record defending religious rights and writing against euthanasia and assisted suicide drawing praise from Republicans and evangelicals.

Announcing the selection in the White House on Tuesday night, Trump said Gorsuch was "as good as it gets".

He told the packed room: "Judge Gorsuch has outstanding legal skills, a brilliant mind, tremendous disciple, and has earned bipartisan support.

He added: "Depending on their age, a justice can be active for 50 years. And his or her decisions can last a century or more, and can often be permanent."

Gorsuch is considered a conservative intellectual, known for backing religious rights and writing against euthanasia and assisted suicide. He is seen as very much in the mold of the late Judge Antonin Scalia, a leading conservative voice on the court for decades, whose seat Gorsuch is set to fill.

"I respect ... the fact that in our legal order it is for Congress and not the courts to write new laws," Gorsuch said. "It is the role of judges to apply, not alter, the work of the people's representatives. A judge who likes every outcome he reaches is very likely a bad judge, stretching for results he prefers rather than those the law demands." 

Democrats vowed to fight the nomination after Republicans blocked President Obama's choice after Scalia died in February 2016.

The Senate's top Democrat, Chuck Schumer, indicated his party would mount a procedural hurdle requiring 60 votes in the 100-seat Senate rather than a simple majority to approve Gorsuch, and expressed "very serious doubts" about the nominee.

Trump's Republicans hold a 52-48 Senate majority, meaning some Democratic votes would be needed to confirm his pick under current rules. 

According to Reuters, his nomination is seen by the White House as a significant departure from Supreme Court nominations from the recent past, given that many justices have come from the eastern United States. Gorsuch lives in Boulder, Colorado, where he raises horses and is a life-long outdoorsman. 

He became the youngest US Supreme Court nominee since Republican President George H.W. Bush in 1991 selected conservative Clarence Thomas, who was 43 at the time. Gorsuch was in the same 1991 graduating class from Harvard Law School as Obama.

The selection of Gorsuch, who was on a list of about 20 judges suggested by conservative legal activists, unified Republicans in a way not seen since Trump's November 8 election victory, with even critics within the party such as South Carolina Senator Lindsey Graham singing the nominee's praises.

Trump made his choice between two US appeals court judges, Gorsuch and Thomas Hardiman of the Philadelphia-based 3rd US Circuit Court of Appeals, according to a source involved in the selection process.

The Senate confirmed Gorsuch for his current judgeship in 2006 by voice vote with no one voting against him.

Democrats signaled it may not be easy this time.

"Judge Gorsuch has repeatedly sided with corporations over working people, demonstrated a hostility toward women's rights, and most troubling, hewed to an ideological approach to jurisprudence that makes me skeptical that he can be a strong, independent justice on the court," Schumer said.

Trump got the opportunity to name Scalia's replacement only because the Republican-led Senate, in an action with little precedent in US history, refused to consider Obama's nominee for the post, appeals court judge Merrick Garland. Obama nominated Garland on March 16 but Republican senators led by Majority Leader Mitch McConnell denied Garland the customary confirmation hearings and vote.

"This is the first time in American history that one party has blockaded a nominee for almost a year in order to deliver a seat to a president of their own party. If this tactic is rewarded rather than resisted, it will set a dangerous new precedent in American governance," Oregon Democratic Senator Jeff Merkley said. 

If confirmed, Gorsuch would expand the court's conservative wing, made up of John Roberts, Anthony Kennedy Samuel Alito and Thomas. Kennedy long has been considered the court's pivotal vote, sometimes siding with the liberals in key cases such as the June 2016 ruling striking down abortion restrictions in Texas.

The court's restored conservative majority likely would be supportive toward the death penalty and gun rights and hostile toward campaign finance limits. Scalia's replacement also could be pivotal in cases involving abortion, religious rights, presidential powers, transgender rights, voting rights, federal regulations others.

As long as Kennedy and four liberals remain on the bench, the court is not expected to pare back abortion rights as many US conservatives fervently hope. The Supreme Court legalized abortion in the landmark 1973 Roe v. Wade ruling. In June, the justices ruled 5-3 to strike down a Texas law that restricted abortion access, with Kennedy and the liberals in the majority. 

Trump may get to make additional appointments. Liberal Justice Ruth Bader Ginsburg, who Trump called upon to resign last July after she called him "a faker," is 83 while Kennedy is 80. Stephen Breyer, another liberal, is 78.

Additional reporting from Reuters.