McMonagle first stood as a candidate for Sinn Féin at the 1999 Donegal County Council election.[5] Though not elected, he did secure his deposit - which was lost by Fine Gael candidate Paddy Gildea.[6]
At the 2004 Letterkenny Town Council election, with nine seats available, McMonagle finished in seventh place - his first electoral success. He joined Damien Blake and Neil Clarke as new members of Letterkenny Town Council.[7]
At the 2014 Donegal County Council election, with ten seats available, McMonagle finished in sixth place, trailing James Pat McDaid, Ian McGarvey, John O'Donnell, Ciaran Brogan and Liam Blaney, and secured election to Donegal County Council for the first time.[8]
As mayor, McMonagle was photographed walking around Derry with Taoiseach Leo Varadkar on an official visit by the Taoiseach across the border in 2017, prompting an angry response from a niece of Cummings.[1][4] When contacted, no comment from Varadkar was forthcoming.[1]