On Thursday, Dec 17, the DUP’s 90-member executive ratified her appointment after the party's MPs and assembly members elected the current Northern Ireland finance minister during a meeting at the Park Avenue Hotel in east Belfast
Following in the footsteps of Robinson and Reverend Ian Paisley, Foster said it was an "enormous honor and an even greater responsibility" to take on the role.
She was the only candidate standing for the leadership following a shock announcement by the party’s deputy leader Nigel Dodds that he would not seek the role. It had been expected that Dodds would take over the leadership and appoint Foster as First Minister.
She will officially take over when Robinson stands down on January 11 upon the Northern Ireland Assembly’s return from the Christmas recess.
"It is truly humbling to follow in the footsteps of political giants like Ian Paisley and Peter Robinson," she told the BBC.
"For much of the last 40 years this party toiled in the political wilderness, but today we stand tall as the largest unionist party and the party of Northern Ireland.
"That is down to the hard work and efforts of those who have gone before me.
"And as a result of that labor this role is not just as leader of the DUP but the leader of unionism.
"I want to build on the firm foundations that have been laid and take this party from strength to strength."
Peter Robinson expresses his thanks to the Party and his full support for the new Party Leader Arlene Foster MLA pic.twitter.com/oJ1hIQ9f9U— Brian Kingston (@BrianKingston) December 17, 2015
Formally a member of the Ulster Unionist party, Foster, 45, has been an MLA since 2003.
Foster grew up in a Protestant community in Fermanagh, and she experienced the IRA’s campaign along the border with the Republic firsthand. Her father was aA part-time Royal Ulster Constabulary officer whom the IRA attempted to murder. In addition, she herself survived an IRA bombing when her school bus driver was targeted.
She opposed the Good Friday Agreement in 1998 and was known as one of the “baby barristers” within the UUP who actively opposed leader David Trimble after he supported the Belfast Agreement.
In 2004, Foster defected from the UUP to the DUP where some still regard her as a “blow-in.”
She has fulfilled the role of First Minister twice since joining the DUP, during the Assembly crisis earlier this year and in 2010 when Robinson temporarily stepped aside following a BBC "Spotlight" program which revealed his wife’s affair and allegations that the Robinsons received financial support from property speculators.
The Fermanagh and South Tyrone MLA has also fulfilled the duties of Minister of the Environment and Minister for Enterprise, Trade and Investment before becoming Minister for Finance and Personnel in May 2015.
British Prime Minister David Cameron and Northern Ireland Secretary of State Theresa Villiers have both expressed their good wishes to Foster. Northern Ireland’s Deputy First Minister, Sinn Féin’s Martin McGuinness, also sent his congratulations.
"I will work positively with her for the benefit of all our people," he added.
PM: Congratulations to Arlene Foster on her appt as DUP leader. I look fwd to working with her in building a bright & secure future for NI.— UK Prime Minister (@Number10gov) December 17, 2015
Congratulations to Arlene Foster on her election as the new @DUPleader.I will work positively with her for the benefit of All our people.— Martin McGuinness (@M_McGuinness_SF) December 17, 2015
It had previously been speculated that the role of DUP leader and Northern Ireland First Minister would be separated in the same way that Gerry Adams acts as leader of the Sinn Féin political party but Sinn Féin’s Martin McGuinness holds the title of Northern Ireland Deputy First Minister.