[3] Career Denno worked for Unum for sixteen years, followed by a stint as assistant attorney general of Maine.
[4][5] Denno later became an instructor at Saint Joseph's College of Maine and manager of the Preble Street Soup Kitchen.
[6] He retired from the directorship of the Office for Family Independence within the Maine Department of Health and Human Services in 2013.
[7] Denno contested the open seat of Maine House of Representatives member Steve Moriarty in 2014, losing to Mike Timmons.
[10][11] Following a diagnosis of lung cancer in 2018, Denno announced that he would resign from the state legislature in March 2019 and endorsed Steve Moriarty.