Brian Cowen was voted in to replace Bertie Ahern as Irish prime minister in a parliamentary vote on Wednesday, and later named a new cabinet with a number of changes, the dpa reported.
Cowen, leader of the ruling Fianna Fail party, received 88 votes in favour to 76 against. He was nominated by Ahern, who tendered his own resignation and described Cowen as a "a uniquely well qualified candidate."
Following the vote, the 48-year-old former finance minister went to to Aras an Uachtarain, the residence of Irish President Mary McAleese, to receive his seal of office.
He then returned to parliament in Dublin to announced the new cabinet, which sees several changes from that left by Ahern.
Brian Lenihan was named Minister for Finance - the job held by Cowen before becoming prime minister, while Dermot Ahern was appointed new Minister for Justice, with his position old post of Foreign Affairs taken by Micheal Martin.
Other changes saw Batt O'Keefe made new Minister for Education, taking over from Mary Hanafin, who moves to Social and Family Affairs.
Mary Harney retained her position as Minister for Health as did Willie O'Dea as Defence Minister.
Ahern handed in his resignation to McAleese Tuesday evening, marking the end of almost 11 years at the helm of Irish politics.
He announced his resignation at the beginning of April amid questions about his personal finances.
Fianna Fail, Ireland's largest political party, has been in power since 1997 and was returned to office last May in a coalition with two small parties and a number of independents.