On 29 February 1980, he joined the national broadcaster, Raidió Teilifís Éireann (RTÉ), to present The Weekend Breakfast Show on RTÉ 2fm, and later, shows such as Poparama, The Hotline, Night Train and The Great Giveaway Show. Dempsey later hosted the lunchtime show before moving to the breakfast slot in the mid-1980s. He picked up where Marty Whelan had left off, engaging the audience with his natural personality, a world apart from the 'jocks' that stalked the Radio Centre in Montrose at the time. Apart from a brief time off breakfast following 2fm's 1989 relaunch, he has remained on early mornings since. Maxi was placed on the breakfast show at that time, but, after a few weeks, it was apparent to all that her style was not suited to the format; Dempsey was promptly reinstated.