Crime journalist Paul Williams will join Newstalk as part of a new breakfast show team that also includes Shane Coleman, Colette Fitzpatrick and former rugby player Alan Quinlan.
As part of a string of changes to the Newstalk schedule, political journalist Sarah McInerney also joins the radio station and will co-present a drivetime programme with Chris Donoghue from 4pm.
Pat Kenny's show will begin one hour earlier at 9am and run for an additional half hour, while the current drivetime host George Hook will present a two-hour programme from noon to 2pm. The changes apply from September.
Williams, whose books include Evil Empire and Murder Inc, has written about crime for several Irish newspapers, most recently the Irish Independent. He has made several documentaries for TV3.
Fitzpatrick is best known for her role as a news and current affairs presenter on TV3, though since last summer she has hosted a Sunday morning programme on Newstalk. The presenter, who began her career in radio, will continue to work for TV3.
Coleman currently presents the Sunday Show on Newstalk but is a regular stand-in host on other programmes. The breakfast team will work "on a rotating schedule", the station said.
The changes follow the departure from the station of Ivan Yates, who co-presented Newstalk Breakfast, Newstalk's most popular programme, alongside Donoghue.
McInerney is the political correspondent for the Sunday Times in Ireland and has regularly appeared on television and radio as a political expert.
Sean Moncrieff’s afternoon slot has been cut by one hour and will run from 2pm to 4pm under the new schedule. The one-hour lunchtime news show, presented by Jonathan Healy, will disappear from the daily schedule. The station said Healy would “remain a part of the Newstalk team”.
Newstalk chief executive Tim Collins, who joined the company earlier this year, said the new appointments would "add further momentum" to the station's ambition to overtake the number of listeners RTÉ Radio 1 has in the 25-54-year-old age group.
Newstalk, which has a 6.2 per cent share of the national radio market and some 379,000 daily listeners, is owned by Denis O'Brien's Communicorp group, which also owns Today FM, Dublin's 98 FM and the music stations Spin 1038 and Spin SouthWest.
