Dennis was hired by the City of Puyallup (WA) in 1987, worked his way through the ranks, and retired in 2022 in the position of Battalion Chief with Central Pierce Fire and Rescue (Pierce County Professional Fire Fighters IAFF Local 726). During his active career he served continuously on the Local 726 Executive Board, holding all elected positions.
In 1994 Dennis was elected as Trustee for the Washington State Council of Fire Fighters (WSCFF), and remained in that position until 2001, when he was elected to the WSCFF Executive Board. In 2007 he was elected WSCFF Vice President, an office he held until February 2016 when he assumed the duties of WSCFF President. Dennis was elected as WSCFF President in June of 2016. In 2024 the WSCFF honored Dennis with the Walt Lamber Trade Union Leadership Award.
On the national level, Dennis served as an IAFF State Service Representative for the State of Washington for over 25 years, an IAFF Educational Instructor for nearly 15 years, and currently presides as the elected Chairman of the Federation of State Provincial Professional Fire Fighters, where he facilitates the gathering of the state and provincial leaders on a biannual basis.