Dennis is of both Aboriginal and Torres Strait Islander heritage and comes from Darwin in the Northern Territory. He belongs to the Wardaman, Luritja and Warramunga people of the NT and the Wagadagam people of the Torres Strait. He has worked for the Australia Council for the Arts as a Project Officer for the Aboriginal and Torres Strait Islander Arts Board (ATSIA). There, he worked to deliver a strategic development plan to help Indigenous Arts organisations get better outcomes.
Between 2010 and 2012, Dennis worked as Content Division Manager at National Indigenous Television (NITV) and was then appointed to the role of National Indigenous Program Manager at the Australian Film Television and Radio School (AFTRS). In his time at AFTRS, Dennis oversaw a large growth in Indigenous participation and workshops in arts media throughout Australia.
Dennis is currently the Chief Executive Officer of Mimi Ngurrdalingi Aboriginal Corporation (MNAC) which includes Mimi Aboriginal Arts, and provides and manages arts ventures and programs throughout the Katherine region.