Arlene Foster has described it as a "huge honour" to lead the Democratic Unionist Party.
The Stormont Finance Minister was the sole candidate to replace Peter Robinson and was formally elected following a meeting of DUP Assembly members and MPs today.
The 45-year-old mother of three is the DUP's first female leader and will become the first woman to lead Northern Ireland when she takes on the role of First Minister next month.
She said: "It is an enormous honour and an even greater responsibility to take up this role.
"It is truly humbling to follow in the footsteps of political giants like Ian Paisley and Peter Robinson."
Two others, DUP deputy leader Nigel Dodds and Sammy Wilson, had ruled themselves out of the leadership race and Ms Foster received almost unanimous support.
In her inaugural speech at the Park Avenue Hotel in east Belfast, Mrs Foster said: "The style of leadership may change but the fundamental values of this party will not.
"I want to take our cause and our case to every part of the province.
"I want to make the case for the Union to every class and creed.
"I want us to help make the lives of our people better."
The Fermanagh and South Tyrone MLA made a high-profile defection from the Ulster Unionist Party in 2004 citing difficulties with the early release of paramilitary prisoners as part of the Good Friday peace agreement and the decision to share power with Sinn Fein.
Having grown up on the border with the Irish Republic, she has first hand experience of the bloody sectarian violence which has plagued Northern Ireland.
Her police officer father was shot by the IRA when she was aged just eight and as a teenager she survived a republican bomb attack targeting the driver of her school bus in 1988.
She added: "The Troubles have scarred Northern Ireland's history but we must not let them shape our future. We have an opportunity to build the best legacy possible to those who lost their lives during the Troubles - a prosperous Northern Ireland, confident, outward looking and at peace with itself."
Mrs Foster told the audience she had a positive vision for the future.
"The people of Northern Ireland don't want to hear their politicians squabbling about issues that seem unconnected to their daily lives," she added.
"People who get up early in the morning, get their kids to school, go and do a hard day's work and come home tired, don't want to turn their TVs on and hear us sound completely and utterly out of touch with real life, arguing over things that don't matter to them or their family.
"They want to know that when they work hard and pay their taxes that their government is doing its best to ensure that their children get a good education, that their parents will get the healthcare they need when they need it and that they will be supported if times get tough."
Hinting at a more progressive outlook for the party founded by a firebrand Protestant preacher, Mrs Foster said: " We will never resile from our belief that Northern Ireland is best served being part of the Union. But unionism is about all of us and not anyone alone. It is about everyone working together as one, for the greater good, to build a Northern Ireland we can all be proud of.
"I want people of all religious persuasions, from all social backgrounds to make this party their home because we are the ones who can create a growing economy, who can best reform our NHS and who can tackle educational underachievement in our working class communities."
Mr Robinson, 66, announced his intention to resign as DUP leader and Stormont First Minister last month, days after signing a political deal with Sinn Fein and the British and Irish Governments to stabilise the rocky power-sharing administration in Belfast.
Prime Minister David Cameron and Northern Ireland Secretary Theresa Villiers were among the first to offer congratulations.
Mr Cameron said on Twitter: "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."
Ms Villiers said she was sure the new DUP leader would be "committed to doing the right thing for everyone in Northern Ireland.
Stormont's Deputy First Minister Martin McGuinness of Sinn Fein also used social media to welcome the new appointment.
He said on Twitter: "Congratulations to Arlene Foster on her election as the new @DUPleader. I will work positively with her for the benefit of All our people."
Irish Taoiseach Enda Kenny said he looked forward to continuing the strong working relationship established during Mrs Foster's time as a minister.
He also said he hoped the positive relationship that exists between the Irish Government and the Northern Ireland Executive would develop further.