Closely concerned with matters of ethics and poverty, Lunn became a Christian socialist, testifying the social gospel from the pulpit. Seeking to eliminate suffering through structural change, Lunn joined the Socialist Party of America and in 1911 he was elected Mayor of Schenectady at the head of the local Socialist ticket. His term was marked by a commitment to expansion of the city's parks and playgrounds, establishment of city health centers, and improvements in the local system of public schools and in garbage collections—the classic range of practical programmatic interests later known as sewer socialism.