As a councillor, Lunn served as Mayor of Lisburn between 2006 and 2007. [citation needed]
He was elected to the Northern Ireland Assembly for Lagan Valley in the 2007 assembly election. Lunn took over the Alliance candidacy for Lagan Valley from Seamus Close, the longtime representative for the area. While many pundits predicted that Alliance would struggle to hold on to the seat, Lunn's performance saw the new candidate elected fourth out of the six seats available.[1] He retained the seat at the 2011 Assembly election. He is a former chairman of the Alliance Party.[2]
Regarding accusations in 2012 of Sinn Féin infiltrating primary schools, [clarification needed] Lunn said, "In the context of Lumen Christi as a highly successful grammar school which has taken a public stance on the question of academic selection, in defiance of the minister's instruction and indeed the view of the Catholic Church, it is hard to see these appointments as anything other than a means of infiltration of the school's board of governors, with the aim of influencing the stance taken by the present board."[4]
On 2 March 2020, Lunn announced that he was leaving the Alliance Party due to "internal difficulties"; he continued to sit as an independent MLA.[5]
He later announced that he would not be contesting the 2022 Northern Ireland Assembly election.[6]
