It is a common expression in sports reporting. Although there are earlier similar phrases, it is commonly attributed to writer/broadcaster Dan Cook; his original line was "The opera ain't over till the fat lady sings."

This occurred in April 1978, when he coined the phrase after the first basketball game between the San Antonio Spurs and the Washington Bullets (now the Washington Wizards) during the 1977-78 National Basketball Association playoffs, to illustrate that while the Spurs had won once, the series was not over yet.

The phrase has also been attributed to former major league manager Earl Weaver. However, it is now known that Cook did not coin the phrase; Fred R. Shapiro found and published an example in The Yale Book of Quotations which appeared in the Dallas Morning News on 10 March 1976:

Despite his obvious allegiance to the Red Raiders, Texas Tech sports information director Ralph Carpenter was the picture of professional objectivity when the Aggies rallied for a 72-72 tie late in the SWC tournament finals. "Hey, Ralph," said Bill Morgan, "this... is going to be a tight one after all." "Right," said Ralph. "The opera ain’t over until the fat lady sings."

In the same newspaper on 26 November 2006, Steve Blow followed up the discovery by contacting Bill Morgan about the incident: "Bill vividly remembers the comment and the uproar it caused throughout the press box. He always assumed it was coined on the spot. 'Oh, yeah, it was vintage Carpenter. He was one of the world’s funniest guys,' said Bill, a contender for that title himself."

A suggestion that the phrase is older is based on an old saying in the Southern United States stating that "Church ain't over until the fat lady sings". This form of the line was apparently well known in the South for years, appearing in a 28 page booklet in 1976 entitled Southern Words and Sayings.