Pat Kenny is to leave RTÉ and will take up employment with Newstalk, ending a 41-year career with the national broadcaster.
Mr Kenny, 65, will not be renewing his contract with RTÉ and will leave with immediate effect.
RTÉ Director General Noel Curran paid tribute to his contribution to public service broadcasting, describing him as a "versatile and popular broadcaster".
"Pat Kenny's contract with RTÉ expired earlier this year and we have been aware for some time that he had an offer from commercial radio.
"Through lengthy negotiations every effort was made to retain Pat's services but unfortunately we could not come to an agreement," Mr Curran said.
The Director General said RTÉ will now focus on refreshing the Radio 1 schedule on the back of strong listenership figures last week.
Mr Kenny presented numerous highly-rated news and current affairs programmes in RTÉ across four decades.
Among the shows he presented were Today with Pat Kenny, The Late Late Show, Kenny Live, Frontline and Today Tonight.
He was also co-presenter of the Eurovision Song contest in 1988.
Mr Kenny has courted controversy in recent years given the scale of his salary at a time when RTÉ was attempting to reduce its deficit and presenter salary scales.
His salary was €630,000 in 2011, €729,604 in 2009 and €950,976 in 2008.
Newstalk said Mr Kenny would be on air from 2 September.
He will present a current affairs show every weekday from 10am to 12.30pm.
In a statement, Pat Kenny said: "Like many of my colleagues, I have always regarded Newstalk as a valuable source of news and comment.
"I am delighted to have the opportunity to contribute to the growth of Newstalk and to be part of a new team where, hopefully, my experience will also add value.
"I am relishing the challenge ahead and looking forward to a new chapter in my career, with the world of independent broadcasting, helping to develop Newstalk into the talk radio of choice for listeners countrywide."
Newstalk Station Editor Garrett Harte said: "Pat Kenny's arrival marks a significant milestone for Newstalk and reflects our long-term commitment to the development of independent radio, in Ireland."