For two years Chaplin worked in the strike committee with Mother Jones for the bloody Kanawha County, West Virginia strike of coal miners in 1912-13. These influences led him to write a number of labor oriented poems, one of which became the words for the oft-sung union anthem, Solidarity Forever.
Chaplin then became active in the Industrial Workers of the World (the I.W.W., or "Wobblies") and became editor of its eastern U. S. publication "Solidarity". In 1917 Chaplin and some 100 other Wobblies were rounded up, convicted, and jailed under the Espionage Act for conspiring to hinder the draft and encourage desertion. He served four years of a 20-year sentence for this.
Although he continued to work for labor rights after his release from prison, Chaplin was very disillusioned by the aftermath of the Russian Revolution; however, he was also not pleased by the course of New Deal liberalism. He became active in the cause of preventing communist infiltration in American unions.
Eventually Chaplin settled in Tacoma, Washington where he edited the local labor publication. From 1949 until his death he was curator of manuscripts for the Washington State Historical Society.