MacCartney was named as a candidate for legislature by the Massachusetts Social Democratic Party in the November 1899 election, running against a former state legislator in the 4th Plymouth District, previously regarded as conservative and solidly Republican."Election News," Appeal to Reason [Girard, KS], whole no. 208 (Nov. 25, 1899), pg. 2. Social Democrats worked hard over the course of several weeks holding a series of rallies were held in the three towns of the district — Rockland, Hanover, and Hanson — with MacCartney ultimately emerging victorious in the three-way race by a plurality of 102 votes. The unexpected result was met with jubilation by MacCartney's supporters, with one group parading a banner through the streets of Rockland with a banner inscribed, "What's the matter with MacCartney? He's all right."
