"The Party Chairman has received a letter from Sir Jeffrey Donaldson MP confirming that he has been charged with allegations of an historical nature and indicating that he is stepping down as leader of the Democratic Unionist Party with immediate effect," the DUP said in a statement.
"In accordance with the party rules, the party officers have suspended Mr Donaldson from membership, pending the outcome of a judicial process."
It appointed Gavin Robinson, a fellow member of the British parliament, as interim party leader.
As a member of the London parliament, Donaldson, 61, does not hold a position in the Northern Irish power-sharing government, a key part of the region’s 1998 peace settlement that only resumed last month following a two-year suspension.
His resignation comes amid a tumultuous period for the DUP and with elections to the British parliament expected later this year.
Sinn Fein overtook the DUP for the first time at elections to the Northern Irish assembly in 2022, paving the way for Michelle O’Neill to become the British region’s first Irish nationalist First Minister.
Donaldson was the third person to lead the DUP in a matter of weeks when he took over in 2021 after the party in effect dumped both his predecessors.
He also had to face down some opposition from within the party last month when the DUP decided to end its boycott of the power-sharing government over post-Brexit trade rules.
All the lawmaker’s social media accounts appeared to have been deleted, with Donaldson’s handle on the social network X showing the message "This account doesn’t exist".
