Sir Jeffrey Donaldson has been charged with historical sexual offences and has resigned as Democratic Unionist Party (DUP) leader.
A 57-year-old woman has also been charged with aiding and abetting in connection with the alleged offences.
They were both arrested on Thursday morning by PSNI detectives and were questioned before being charged on Thursday night.
They are now due to appear in court next month.
In a statement the DUP said: "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.
"In accordance with the Party Rules, the Party Officers have suspended Mr Donaldson from membership, pending the outcome of a judicial process.
"The Party Officers have this morning unanimously appointed Mr Gavin Robinson MP as the Interim Party Leader."
Police issued a statement on Friday morning, but did not disclose the identity of those charged.
The statement said a 61-year-old man had been charged with "non-recent sexual offences" adding that a 57-year-old woman was also arrested at the same time and charged with "aiding and abetting additional offences".
The statement also confirmed the pair would appear before Newry Magistrates' Court on 24 April.
It is understood DUP officers met on Friday morning after details of the charges emerged.
Sir Jeffrey's social media accounts, including on X, were deleted overnight.
Sir Jeffrey Donaldson was elected leader of the DUP in 2021.
He is also the longest serving MP in Northern Ireland having been first elected to Parliament in 1997.
Sir Jeffrey recently steered his party back in to government in Northern Ireland ending a two year boycott of the Stormont institutions.
The DUP had walked out of government in protest at the Northern Ireland Protocol, claiming the post-Brexit arrangements had undermined their place in the UK.
Sir Jeffrey was first elected to parliament in 1997 as a representative of the Ulster Unionist Party (UUP).
In 2003, following long-standing opposition to the Good Friday Agreement and the leadership of David Trimble, he announced he would leave the UUP, later joining the DUP.
He was awarded a knighthood in 2016 for political service.