The announcement sets Republicans up to change Senate rules -- referred to as the "nuclear option" -- to lowering the threshold of advancing Supreme Court nominees to just 51 votes from 60.
The Senate Judiciary Committee voted 11-9 along party lines to move Gorsuch's nomination to the full Senate.
With Sens. Chris Coons of Delaware, Dianne Feinstein of California, Mark Warner of Virginia and Patrick Leahy of Vermont all saying Monday they could not support Gorsuch, Democrats reached the votes they needed to prevent the advancement of Gorsuch's nomination under current chamber rules.
Republicans, who hold a 52-48 majority, needed a total of 60 votes to end the filibuster. As of Monday afternoon, they had 56 votes, including four Democrats who are voting with them.
Two senators remain undecided. However, even if both were to side with Republicans, it wouldn't be enough to avoid the filibuster.
The majority party can still get around the filibuster by changing Senate rules and using the controversial "nuclear option" to lower the threshold needed to end debate. Democrats, in the face of strong Republican opposition, did the same in 2013 to confirm lower court nominees.
Now Republicans, citing 2013 as a precedent, feel that it's their only choice. But it would permanently nix the filibuster for Supreme Court nominees, essentially giving the party in power all the leverage and eliminating the Senate's tradition of needing at least some bipartisanship to advance such nominees.
Senate Majority Leader Mitch McConnell, should he proceed to the nuclear option, needs only a simple majority of 51 to vote for a change in the rules. It's possible McConnell will have his whole party -- 52 votes -- behind him, but not all Republicans have explicitly said they will back him in the effort.
He can only afford to lose two Republican senators, in which case Vice President Mike Pence would be needed to break a tie. If McConnell loses more than three Republicans, the rule change would not pass.
Pressed by reporters on whether he will vote for the use of the nuclear option, Judiciary Chairman Chuck Grassley refused to explicitly say yes. But he insisted that he is "going to do whatever it takes" to get Gorsuch on the Supreme Court.
Coons, who was the 41st senator to say he plans to take part in the filibuster, told CNN's Wolf Blitzer immediately after his announcement that he understood the consequences of his decision, but also reiterated his pledge that he's open to negotiating with Republicans to find an agreement on avoiding the nuclear option on the next nominee.
"I said, 'I will vote against closure unless the Republicans and Democrats in the Senate can somehow find an agreement that is trustworthy and reliable, where on the next Supreme Court nominee, they won't change the rules and we will have input and a more confirmable, consensus nominee will be put in front of the Senate,'" Coons said. "I'm not saying that I'm insisting that we force the Republican majority to break the rules. That's a choice they're going to have to make."
Warner, the Democrat from Virginia, expressed some semblance hope for a deal.
"I know there are some people still talking so I'll try to keep a little bit of optimism for a couple of more days," he told Blitzer on "The Situation Room."
Sen. Lindsay Graham tried to send some warning shots to Democrats, saying the filibuster will cause Republicans to change the rules in an "unnecessary" move that will "haunt" the Senate for decades.
"To my Democratic colleagues, yeah this is going to be very bad. Let me tell you what's going to happen. The judges are going to become ideological because you don't have to reach across the aisle to get one vote any longer," he told reporters after the hearing. "And every Senate seat is going to become a referendum on the Supreme Court. A lot of us have a tradition of not playing colleagues -- in races involving our colleagues. But now you're telling the country every Senate seat matters. If you want to have a judge in the court, you'd better have a majority. So this is going to haunt the Senate, going to change the judiciary and it's so unnecessary."
The White House is "disappointed" that Democrats will have enough votes to sustain a filibuster against President Donald Trump's Supreme Court nominee Neil Gorsuch, press secretary Sean Spicer told reporters following the filibuster news.
"If the Democrats get their way, and the numbers are looking that way, this is going to be the first successful filibuster of a nominee to join the Supreme Court, which is clearly unprecedented," Spicer said, adding, "With a vote on Judge Gorsuch on Friday, the American people see which senators are willing to keep this seat open to get in the way of President Trump making progress on one of his most significant choices so far."
Knowing full well that the filibuster would likely lead to Republicans using the "nuclear option," Leahy shared his struggle over his decision but ultimately said he "cannot vote solely to protect an institution," adding that he considers Americans' rights at risk with Gorsuch's nomination.
"I've often said the Senate at its best can and should be the conscience of the nation, but I must first and foremost vote my conscience," Leahy said. "I will not and can not support advancing this nomination."
Judiciary committee vote
Before voting, senators engaged in an at-times testy debate over not only Gorsuch, but Republican action to block President Barack Obama's Supreme Court nominee, Merrick Garland, last year.
"This action by my colleagues was unacceptable and has scarred this process and this body," Coons said in the hearing. "There has never been a partisan filibuster of a Supreme Court nominee in history; and while technically correct, I question what a seven-month refusal to hold a hearing or vote is -- if not the longest partisan filibuster on this committee ever."
Republicans argued that Democrats would essentially oppose any Trump nominee.
"If (Democrats) are going to oppose Neil Gorsuch to the Supreme Court of the United States, they will never vote and never support a nominee of this President. Because in the end, I think that's really what gets their goat the most," said Sen. John Cornyn of Texas. "We keep hearing about Merrick Garland, but I guarantee if Hillary Clinton had the presidency, we'd never hear Merrick Garland's name again because she would have had the opportunity to pick her own nominee to the Supreme Court."
Spending from outside groups has also been a hotly contested debate in Gorsuch's nomination. Democrats have criticized Gorsuch for not speaking out against third-party groups, with undisclosed donors, who have spent millions in support of his nomination.
The debate continued during the hearing Monday.
"This nomination is not the usual nomination. It comes in a different way and it has proceeded in a way of excessive spending of dark money that in the time I have been on this committee I have never seen before," said Feinstein, the top Democrat on the committee.
Committee Chairman Chuck Grassley, however, pointed to liberal groups that supported Supreme Court nominees appointed by Obama, like Garland.
"Now, I've never heard any Democrat complain about all that money that was spent last year," Grassley said.
Independent Sen. Angus King (Maine) -- While King is an independent, he's considered part of the Democratic caucus. He's been fairly quiet about Gorsuch of late. His seat is also considered safe in 2018.
Democrats who will vote for Gorsuch and against filibuster
Sen. Joe Manchin (West Virginia)
Sen. Heidi Heitkamp (North Dakota)
Sen. Joe Donnelly (Indiana)
Democrats who will vote against filibuster
Sen. Michael Bennet (Colorado)
Democrats who plan to filibuster
1. Senate Minority Leader Chuck Schumer (New York)
2. Independent Sen. Bernie Sanders (Vermont)
3. Sen. Bob Casey (Pennsylvania)
4. Sen. Ron Wyden (Oregon)
5. Sen. Patty Murray (Washington)
6. Sen. Elizabeth Warren (Massachusetts)
7. Sen. Jeff Merkley (Oregon)
8. Sen. Tom Carper (Delaware)
9. Sen. Tammy Baldwin (Wisconsin)
10. Sen. Bill Nelson (Florida)
11. Sen. Cory Booker (New Jersey)
12. Sen. Mazie Hirono (Hawaii
13. Sen. Tom Udall (New Mexico
14. Sen. Jack Reed (Rhode Island)
15. Sen. Chris Murphy (Connecticut)
16. Sen. Sheldon Whitehouse (Rhode Island)
17. Sen. Tim Kaine (Virginia)
18. Sen. Kamala Harris (California)
19. Sen. Al Franken (Minnesota)
20. Sen. Debbie Stabenow (Michigan)
21. Sen. Ed Markey (Massachusetts)
22. Sen. Chris Van Hollen (Maryland)
23. Senate Minority Whip Dick Durbin (Illinois)
24. Sen. Jeanne Shaheen (New Hampshire)
25. Sen. Gary Peters (Michigan)
26. Sen. Maggie Hassan (New Hampshire)
27. Sen. Amy Klobuchar (Minnesota)
28. Sen. Martin Heinrich (New Mexico)
29. Sen. Tammy Duckworth (Illinois)
30. Sen. Kirsten Gillibrand (New York)
31. Sen. Richard Blumenthal (Connecticut)
32. Sen. Maria Cantwell (Washington)
33. Sen. Brian Schatz (Hawaii)
34. Sen. Catherine Cortez Masto (Nevada)
35. Sen. Claire McCaskill (Missouri)
36. Sen. Sherrod Brown (Ohio)
37. Sen. Jon Tester (Montana)
38. Sen. Dianne Feinstein (California)
39. Sen. Patrick Leahy (Vermont)
40. Sen. Mark Warner (Virginia)
41. Sen. Chris Coons (Delaware)
42. Sen. Ben Cardin (Maryland)
43. Sen. Bob Menendez (New Jersey)
This story will be updated as CNN receives updated information.