She has officially taken over the post from Peter Robinson
The North's new first minister has described her predecessor as the "most astute" politician in a generation.
Arlene Foster has officially taken over the post from the retiring Peter Robinson.
He said he was stepping down with confidence that the political institutions will be in place for generations to come.
The Taoiseach Enda Kenny has congratulated Ms Foster on her election.
Mr Kenny said she "has proved herself to be highly effective in her roles as Minister for Enterprise, Trade and Investment and Minister for Finance and Personnel and is sure that she will continue to work hard for the people of Northern Ireland as she takes on the huge responsibility of the First Minister role".
He has also paid tribute to her predecessor, Mr Robinson, thanking him for his very significant contribution to the Northern Ireland peace process.
The 45-year-old from Co Fermanagh is the first woman to lead Northern Ireland's powersharing executive.