He graduated from University College Dublin with a degree in History and Politics.[4] He then obtained a postgraduate in journalism from the National Institute for Higher Education and in accounting and finance from the Association of Chartered Certified Accountants.[5][6]
Whelan began his career in journalism in the mid-1980s as a freelance feature writer with Magill and the Irish Independent, before working as a reporter in London on the business newspaper, Marketing. He moved back to Ireland in the early 1990s and worked as a business journalist at The Sunday Tribune.[7]
He joined RTÉ in 1991 at the same time as Mark Little, Rachael English and Paul Reynolds.[8] Whelan worked in a number of areas, including the foreign desk, serving as the deputy foreign editor.[9] He has reported from wars in Bosnia and Kosovo and on the return of Hong Kong to the People's Republic of China.[4]
Whelan was based in Brussels from 1999.[9] In 2001, he became Europe Correspondent,[10] and was appointed Europe Editor in 2003.[9] After the resignation of George Lee as Economics Editor to begin a career in politics, Whelan became Economics Correspondent.[11]
In March 2019, it was announced that he would succeed Fiona Mitchell as the London correspondent for RTÉ News.[12]
On 21 January 2022, it was announced by RTÉ that Whelan would succeed Brian O'Donovan as the new Washington correspondent from February 2022.[13]
On 28 April 2026, it was announced that he would return as the London correspondent for RTÉ News, succeeding Tommy Meskill.[6][14]