A founder member of the Scottish Labour Party in 1888 and of the Independent Labour Party in 1893, Smillie was a close associate of Keir Hardie during their early careers and remained friends until Hardie's death in 1915. He campaigned for Hardie in many of his election contests, including the first in 1888. Smillie stood for parliament on seven occasions between 1894 and 1910. Later, he could have had the nomination for winnable seats in Glasgow; but chose to remain with his work for the miners.