The singer's hit "Bad Guy" has also landed Eilish in the record books - no artist has ever spent nine weeks at number two before hitting the top of the Billboard Hot 100 countdown.
At 17, she also becomes the first person born this century to hit number one, and the youngest since Lorde took "Royals" to the top in 2013.
Gracious Lil Nas X was quick to salute Billie on Twitter, writing, "congratulations to billie eilish!! u deserve this!!"
He still has at least one more week of celebrations - "Old Town Road" also becomes the first single to top the U.S. Streaming Songs chart for 20 weeks, and it's one week away from tying Luis Fonsi and Daddy Yankee's 17-week run on the Digital Songs Chart with "Despacito".