"Old Mother Leary" was built on the music of a slightly older song, "A Hot Time in the Old Town." Whoever wrote the words for "Old Mother Leary" just dropped the older song's verses and borrowed the melody of the chorus, along with its tagline:
When you hear dem a bells go ding, ling ling
All join 'round and sweetly you must sing
When the verse am through, in the chorus all join in,
There'll be a hot time in the old town tonight.
Written by Theodore August Metz and Joseph Hayden, "A Hot Time in the Old Town" brought together two musical genres—one old and one new. Metz and Hayden were performers in the McIntyre and Heath Minstrels and part of a musical tradition that dated to the 1820s. Minstrel shows featured white performers in blackface who sang and danced in a style believed typical of African-American slaves. The racist parodies unfortunately remained popular in all parts of America into the 20th century, well after slavery was outlawed in the United States during the Civil War.
While the Metz and Hayden song quickly became a minstrel show standard, it was composed along the more modern lines of ragtime music. Ragtime seems to have been developed by traveling piano performers in the South and Midwest. The center of the musical style was Missouri, and the most famous ragtime composer was Texas-born Scott Joplin. Ragtime attached an uneven, ragged rhythm to more traditional march music. The resulting up-tempo, syncopated music became especially popular during the 1890s; thousands of people heard the music for the first time at the Chicago World's Fair in 1893.
Ragtime remained popular well into the 20th century, but during the 1920s, jazz replaced ragtime as America's favorite form of popular music.