The 49-year-old appeals court judge from Colorado is being sworn in after a bruising fight that saw Republicans change the rules for approving high court picks - over the fierce objection of Democrats.
The first ceremony took place privately in the Justices' Conference Room, with Chief Justice John Roberts administering the oath required by the Constitution.
Gorsuch's wife, Marie Louise, held the family Bible and all eight of the current justices were present, said court spokeswoman Kathy Arberg. Also in attendance was Maureen Scalia, widow of the late Justice Antonin Scalia, along with her eldest son Eugene.
Later, Gorsuch will appear at a public White House ceremony, where Justice Anthony Kennedy is to administer the oath set by federal law, the last part of the formal process of putting a new justice on the court. Gorsuch, who once clerked for Kennedy, will be the first member of the court to serve alongside his former boss.
Gorsuch will fill the nearly 14-month-old vacancy created after the death of Scalia, who anchored the court's conservative wing for nearly three decades before he died unexpectedly in February 2016. In nominating Gorsuch, President Donald Trump said he fulfilled a campaign pledge to pick someone in the mold of Scalia.
During 11 years on the federal appeals court in Denver, Gorsuch mirrored Scalia's originalist approach to the law, interpreting the Constitution according to the meaning understood by those who drafted it. Like Scalia, he is a gifted writer with a flair for turning legal jargon into plain language people can understand.
Gorsuch will be seated just in time to hear one of the biggest cases of the term: a religious rights dispute over a Missouri law that bars churches from receiving public funds for general aid programs.
His 66-day confirmation process was swift, but bitterly divisive. It saw Senate Republicans trigger the "nuclear option" to eliminate the 60-vote filibuster threshold for all future high court nominees. The change allowed the Senate to hold a final vote with a simple majority.
Most Democrats refused to support Gorsuch because they were still seething over the Republican blockade last year of President Barack Obama's pick for the same seat, Merrick Garland. Senate Republicans refused to even hold a hearing for Garland, saying a high court replacement should be up to the next president.
The White House swearing-in ceremony is a departure from recent history. Justices Sonia Sotomayor and Elena Kagan were both sworn in publicly at the Supreme Court. Former Justice John Paul Stevens has argued that holding the public ceremony at the court helps drive home the justice's independence from the White House.
Some interesting facts about Gorsuch and the court:
- He is the youngest nominee since Clarence Thomas, who was 43 when confirmed in 1991.
- The Colorado native went to high school in Washington while his mother served as EPA administrator in the Reagan administration.
- He's the sixth member of the court who attended Harvard Law School; the other three got their law degrees from Yale.
- Gorsuch credits a nun with teaching him how to write. He and his family attend an Episcopal church in Boulder, though he was raised Catholic and attended Catholic schools as a child. He joins a court that has five Catholics and three Jews.
- As an associate justice, Gorsuch will earn $251,800 a year - more than 15 percent higher than his $217,600 salary as an appellate judge.
- Gorsuch joins the ranks of justices who are millionaires. He reported financial assets in 2015 worth at least $3.2 million, according to his latest financial disclosure report.
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