Nicknamed "Marmite Mary" because she divides opinion sharply, Ms McDonald is the TD (member of the Irish Parliament) for Dublin Central and began her political life as a member of Fianna Fail, one of Ireland's two mainstream political parties.
Addressing the Belfast meeting, Ms McDonald said she believes her leadership will mark a defining chapter in the achievement of a United Ireland.
Mrs McDonald called on supporters at Sinn Fein's AGM to "build our new Ireland", and a special party conference to ratify a new leader will be held on 10 February.
Current deputy leader Ms McDonald said that while nobody could fill the shoes of Republican veteran Mr Adams, "the news is that I brought my own".
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The pair attended Thomas Mills High School in Framlingham, and have been dating for around two-and-a-half-years. Countless newlyweds have chosen Ed Sheeran's ballad, "Thinking Out Loud", to play during their first dance.
"Uniting this island is the best outcome for all our citizens and it is now our task to convince our unionist friends and neighbours of that and to encourage them to help us build a new Ireland".
Sky News Ireland Correspondent David Blevins said the change in leadership was "significant", adding that Mrs McDonald is the first woman to lead Sinn Fein and comes from a middle class background.
She also said: "I believe we are capable of achieving anything that we set our minds to".
I am proud and honoured to be nominated for Uachtarán Shinn Féin.
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So yes, this is possible. "Everybody's Facebook traffic has been declining all year, so they've been de-emphasising news ". The social media platform wants to get back to basics i.e.to focus overwhelmingly on communication between user .
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Hawaiians have been told that they'll have 20 minutes to seek shelter if a missile were launched from North Korea . He said he was still in bed when the phone started going off "like insane ". "Haha glad to know we'll all be safe".