President Mary McAleese and Prime Minister Brian Cowen both phoned to congratulate Harrington after he overcame a wrist injury and gusting, wet conditions to become the first Irishman to win two British Opens.
"The whole country is hugely proud of Padraig's success and the manner in which he achieved it. Once again, he has combined tremendous natural talent with hard work, dedication and resilience," said McAleese, Ireland's symbolic head of state.
Pubgoers watching the tournament live on television in Dublin pubs exchanged toasts and high-fives as Harrington eagled the 17th hole to put his victory beyond doubt.
"Padraig is fast becoming Ireland's greatest-ever golfer," said Irish sports minister Martin Cullen, who called Harrington "a wonderful Irishman and a magnificent sporting ambassador for Ireland."
Cowen said Harrington's initial win last year was "quite an achievement. However to retain the title in such difficult weather conditions, and also carrying an injury, shows that Padraig is a golfer in his prime and at the top of his profession."
Harrington is the only citizen of the Republic of Ireland ever to win the 148-year-old competition. The only previous Irish winner, Fred Daly in 1947, came from the British territory of Northern Ireland.