I remember my mom using this phrase when I was young. Most often it was in the context of me not doing my chores in a responsible, "This is not the Life of Riley, Mary." Although I do remember asking once what it meant, and although I did understand, contextually, what Mom meant, I really don't remember where the phrase came from.
So today, in typical sound like mother style, I used that phrase on my daughter.
I was quickly inspired to do a google search to investigate the origins of "the Life of Riley."
From several sources I learned that most agree the phrase originated among Irish American immigrant in the early decades of the 20th Century. It appears to have been in somewhat common use among Irish American immigrants by the nineteen teens.
There seem to be some earlier references to a wealthy Riley or Reilley or O'Reilly in song and theater, but nothing that seems to be generally acknowledged as the source of the phrase. The most well known of these was in a Vaudeville song by Pat Ronney in the 1890s, in which Mr. Reilley is a wealthy hotel keeper.
The earliest written reference appears in a Hartford Courant article, in December 1911; the author has the phrase in quotes as one might a new or less familiar idiom.
Later, the phrase commonly used among Irish American soldiers in World War I.
And finally, the phrase came into popular use because of a radio and TV character, Chester A. Riley. The radio show began in the 1940, with a feature film coming in 1949, followed by the television series that ran for seven seasons.
And there you have it, The Life of Riley.