Timeline
| 1909 | October 11 - The Man Who Owns Broadway opens at New York Theatre for a 128 show performance run. |
| 1910 | Begins his career as a movie house intermission pianist for silent movie theatres |
| 1910 | Writes the first of many Irish ballads, MOTHER MACHREE |
| 1911 | May 5 - James Bland dies in Philadelphia, PA from tuberculosis |
| 1911 | September 25 - The Little Millionaire opens at George M. Cohan Theatre for a 192 show performance run |
| 1911 | "Life's a Funny Proposition" reaches #5 on the Billboard charts with a recording by George M. Cohan |
| 1911 | MOTHER MACHREE reaches the #1 spot on the Billboard charts with a recording by John McCormack |
| 1911 | January 30 - Barry of Ballymore opens at the Grand Opera House |
| 1911 | MOTHER MACHREE is a #1 hit on the Billboard pop charts twice with separate recordings by John McCormack and Will Oakland |
| 1911 | I LOVE THE NAME MARY reaches #1 on the pop charts with a recording by Will Oakland |
| 1912 | Revival of Forty Five Minutes from Broadway at George M. Cohan's Theatre |
| 1912 | Writes the legendary standard WHEN IRISH EYES ARE SMILING |
| 1912 | February 15 - Macushla opens at the Grand Opera House |
| 1913 | Hired as a song plugger for music publishing company Waterson, Berlin and Snyder |
| 1913 | Chauncey Olcott's cover recording of MOTHER MACHREE reaches the top ten on the pop charts |
| 1913 | WHEN IRISH EYES ARE SMILING reaches the #1 spot on the Billboard charts with a recording by Chauncey Olcott |
| 1913 | January 27 - The Isle of Dreams opens at Grand Opera House |
| 1913 | Chauncey Olcott's recording of MOTHER MACHREE reaches #7 on the pop charts |
| 1913 | WHEN IRISH EYES ARE SMILING reaches #1 on the pop charts with a recording by Chauncey Olcott |
| 1914 | Charter member of American Society of Composers, Publishers and Authors (ASCAP). |
| 1914 | The American Society of Composers, Publishers and Authors (ASCAP) is formed and Harris is its first secretary. Harris would remain on the board until 1924 |
| 1914 | Is a charter member of the American Society of Composers, Authors and Publishers (ASCAP) |
| 1914 | December 25 - Hello Broadway opens at the Astor Theatre for a 123 show performance run |
| 1914 | Begins private study on the piano and singing |
| 1914 | July 26 - Ralph Blane is born in Broken Arrow, Oklahoma |
| 1914 | Contributes songs to the Broadway production Shameen Dhu |
| 1914 | November 23 - The Heart of Paddy Whack opens at Grand Opera House |
| 1914 | Charter Member of the American Society of Composers, Authors and Publishers |
| 1914 | Charter member of the American Society of Composers, Authors and Publishers (ASCAP) |
| 1915 | Founds the New England Poetry Club and served as its first president |
| 1915 | Harris songs appear in the film scores for Always in the Way, Hearts of Men and When it Strikes Home |
| 1915 | "My Little Girl" reaches #2 on the Billboard charts with a recording by Henry Burr & Albert Campbell |
| 1915 | Joins the US Army's Morale Division in Fort Greenleaf, George |
| 1915 | Begins playing the piano in local movie houses for silent pictures |
| 1915 | George MacFarlane's recording of LITTLE BIT OF HEAVEN reaches the #1 spot on the Billboard charts |
| 1915 | Taylor Trio's cover of the 1911 #1 hit MOTHER MACHREE reaches #5 on the Billboard charts |
| 1915 | The Taylor Trio's cover recording of the 1911 #1 hit song MOTHER MACHREE reaches #5 on the pop charts |
| 1916 | Harris songs appear in the film score for Should a Baby Die? |
| 1916 | Produces The Cohan Revue |
| 1916 | Enlists in the US Army where he befriends another young composer, Irving Berlin. The two would write a #2 hit song inspired by their Army days, HOME AGAIN BLUES |
| 1917 | Harris Songs appear in the film score for The Barker |
| 1917 | In the year of it's publication, "Over There" has 2 #1 recordings on the Billboard charts by Nora Bays and the Peerless Quartet. |
| 1917 | With the onset of World War I, the Prince's Orchestra revives "You're a Grand Old Flag." The recording would reach #7 on the Billboard charts |
| 1917 | Enrolls at the New England Conservatory to study music under the tutelage of Stuart Mason |
| 1917 | John McCormack's cover of the 1913 #1 hit song WHEN IRISH EYES ARE SMILING reaches #4 on the pop charts |
| 1917 | John McCormack's cover recording of the 1913 #1 hit song WHEN IRISH EYES ARE SMILING reaches #4 on the pop charts |
| 1918 | Produces The Cohan Revue of 1918 |
| 1918 | Another hit recording of "Over There" by Enrico Caruso tops the Billboard charts at #1 |
| 1918 | Begins performing in night clubs and on lake steamers |
| 1918 | Charles Harrison's recording of DEAR LITTLE BOY OF MINE reaches #6 on the Billboard charts |