Former Mayor Michael R. Bloomberg of New York has qualified for Wednesday’s debate in Las Vegas, the first time the billionaire will appear onstage alongside his Democratic presidential rivals.

A national poll from NPR, PBS NewsHour and Marist released on Tuesday showed Mr. Bloomberg with 19 percent support among Democrats and Democratic-leaning independents, putting him in second place behind Senator Bernie Sanders of Vermont, who had 31 percent. That was a substantial surge since the group’s poll in December, when Mr. Bloomberg received only 4 percent support.

The survey was the fourth national qualifying poll since mid-January that showed Mr. Bloomberg with at least 10 percent support, enough to earn him an invitation to the debate stage before the deadline of 11:59 p.m. Eastern time on Tuesday.

Mr. Bloomberg will face off against Mr. Sanders; Senators Elizabeth Warren of Massachusetts and Amy Klobuchar of Minnesota; former Vice President Joseph R. Biden Jr.; and Pete Buttigieg, the former mayor of South Bend, Indiana.

The debate, which will air on Wednesday at 9 p.m. Eastern time, will be hosted by NBC News, MSNBC, Telemundo and The Nevada Independent.

Mr. Bloomberg’s 19 percent mark was his highest level of support in any debate-qualifying national poll to date. The latest national polling average calculated by The New York Times, which was released late last week, put him at 10 percent nationally, behind Mr. Sanders, Mr. Biden and Ms. Warren.

Mr. Sanders’s support has also increased since the NPR/PBS NewsHour/Marist poll in December, when he had 22 percent. The new poll is the first debate-qualifying national poll released this year showing Mr. Sanders with more than 30 percent support.