Gorsuch's confirmation is a victory for President Trump, who has struggled to achieve his campaign promises of a travel ban from predominantly Muslim countries and health care reform.
At a public ceremony from the White House Rose Garden today, Trump said of Gorsuch's taking a seat on the Supreme Court, "I can say this is a great honor. And I got it done in the first 100 days. That's even nice. You think that's easy."
With Gorsuch, 49, on the court, it is back to its previous balance: four conservatives, four liberals and Justice Anthony Kennedy as the swing vote.
"To my new colleagues and the staff of the Supreme Court, thank you for the very warm welcome. I look forward to many happy years together," Gorsuch said with Trump beaming behind him.
Kennedy administered the oath of office for Gorsuch as his wife, Marie Louise Gorsuch, held the family Bible. The couple's two daughters and Scalia's widow were present for the ceremony. Gorsuch was previously sworn in behind closed doors at the Supreme Court building this morning.
"To the Scalia family, I won't ever forget that the seat I inherit today is that of a very, very great man," Gorsuch said.
But many Democrats argued that Gorsuch's record was too conservative and that he failed to answer key questions about his judicial record during his Senate hearing last month. Many were still upset over Republicans' refusal to bring Garland's nomination up for a vote.
Gorsuch was confirmed by the Senate in a bruising fight after McConnell invoked the so-called nuclear option, which allowed Republicans to end debate with a simple majority, rather than the traditional minimum of 60 votes, and push through the nomination.
Trump gave a shout-out to McConnell, saying, "I especially want to express our gratitude to Sen. Mitch McConnell for all that he did to make this achievement possible."
Gorsuch was a judge on the 10th Circuit Court of Appeals in Denver. He attended Harvard Law School and has a Ph.D. from Oxford, where he was a Marshall scholar. He was nominated by President George W. Bush in 2006 and confirmed by the Senate in a voice vote.
Today had an element of historic significance: Kennedy is the first Supreme Court justice to serve with his or her former law clerk.
"This is a very, very special moment because many years ago, a young Neil Gorsuch started his legal career as a law clerk to Justice Kennedy," Trump said, adding that it's "a fitting testament to Justice Kennedy's impact."
Gorsuch's first big case will be when the Supreme Court hears arguments this month in a case about government funding and religious organizations.
ABC News' Mary Bruce and Audrey Taylor contributed to this report.