The expression suggests an easy life without chores or responsibilities.
The first printed citation of it appears to be from the Connecticut newspaper The Hartford Courant, December 1911, in a piece headed “Bullet Ends Life of Famous Wild Cow.”
“The famous wild cow of Cromwell is no more. After “living the life of Riley” for over a year, successfully evading the pitchforks and the bullets of the farmers, whose fields she ravaged in all four seasons.”
Quote marks around a phrase usually indicate that it’s new and therefore not familiar to readers.
A slightly later instance is from WWI. It appears in a letter from a Sergeant in the American Expeditionary Forces “somewhere in France.” An extract was published in The Brooklyn Daily Eagle in May 1918. The Sergeant wrote that he and his pals were “living the life of Reilly.” Whether that was true or merely propaganda designed to reassure the folks back home isn’t clear. It’s unlikely that any soldier’s life during WWI was a picnic.
Various theories exist as to the origin, such as James Whitcomb Riley’s 1880s poems depicting the comforts of a prosperous home life. It could also have an Irish origin. When the Reilly clan consolidated its hold on County Cavan, they minted their own money, accepted as legal tender even in England. These coins, called “O’Reillys” and “Reilly’s” became synonymous with a wealthy person, and a gentleman freely spending was “living on his Reillys.”
However, Riley’s identity is not known. The lack of any records explaining the source points to the name being chosen as that of a generic Irishman, much as Paddy is used now. The phrase could have been brought to America by Irish immigrants, though there’s no known use of it in Ireland prior to 1918. It could also have originated in the Irish community in America.
There were various Victorian music hall songs that referred to a Reilly living a comfortable and prosperous life. For example, an 1883 song, popularized by the Irish/American singer Pat Rooney, includes in the chorus “Is that Mr. Reilly, of whom they speak so highly?”
However, the phrase “the life of Riley” isn’t found until the early 20th century. It may have been Howard Pease’s popular song, My Name is Kelly, 1919, that brought it to wider public notice.
Everyone will have a different definition of the phrase. But I slept in this morning, had bacon and eggs for breakfast, aced the New York Times crossword puzzle and am now absorbing my wake-up cup of jet fuel, so I know I’m living the life of Riley!