The Cook Islands' prime minister, Jim Marurai, says his coalition government is determined to bring stability, transparent governance and economic growth.
Mr Marurai leads the minority Demo Tumu party in a coalition with the Cook Islands Party.
The 57-year-old has been formally sworn-in by the Queen's representative to become the first national leader from Mangaia.
He was the only candidate to stand in the outlying electorate for the poll in September.
Mr Marurai says many Cook Islanders have been uncomfortable with what he called "the past few weeks of political uncertainty".
Mr Marurai and the former prime minister Dr Robert Woonton split from the Democratic Party last month.