Arvid's parents were general and governor August Aleksander Järnefelt and Elisabeth Järnefelt (née Clodt von Jürgensburg). Arvid had nine siblings: Kasper, Erik, Ellida, Ellen, Armas, Aino, Hilja and Sigrid.
Arvid Järnefelt married Emilia Fredrika Parviainen at Jyväskylä on 6 September 1884. They had five children: Eero, Liisa, Anna, Maija, and Emmi.
Järnefelt became a famous author in the late 19th century. He wrote realistic, often tendentious but psychologically insightful novels, short stories and memoirs.
Arvid Järnefelt became interested in Tolstoyanism, influenced by his mother Elisabeth. He had studied law and 1891 became a trainee lawyer in Vaasa. At the time, he read the writings of Russian author Leo Tolstoy and became fan of Tolstoyanism. Arvid quit his career as a lawyer and began to live as a Tolstoyan; he became farmer at Virkkala. He also helped the poor and prisoners.