Sir Jeffrey Donaldson has been found guilty of 18 historical sex offences, including one count of rape, against two women when they were children.
A jury at Newry Crown Court convicted the former DUP leader, 63, of one count of rape, 13 counts of indecent assault and four counts of gross indecency.
His wife Eleanor Donaldson has been found to have aided and abetted his crimes following a trial of the facts.
Jeffrey Donaldson, dressed in a dark blue suit, white shirt and pink tie, was informed he will be sentenced at the same court later in the year and was remanded in custody.
He showed no reaction to the verdicts when they were read out, as he stood with his hands folded in front of him.
He had pleaded not guilty to the offences, which spanned a period between 1985 and 2008.
Complainants A and B both gave evidence at the trial, alleging they were abused as children.
Jeffrey Donaldson spent two days giving evidence during the trial, where he repeatedly denied the allegations.
Eleanor Donaldson, 60, from Dublinhill Road, Dromore, Co Down, denied several charges of aiding and abetting her husband.
She faced a trial of the facts on mental health grounds, which tested the evidence but could not result in a criminal conviction.
The jury was brought back into the courtroom after lunch on Monday after deliberating for just over 10 hours.
At 2.15pm Donaldson was asked to stand as the court clerk asked the foreman of the jury to read the verdicts.
After the verdicts were delivered, Judge Paul Ramsey expressed his “gratitude and thanks” to the jury.
Before they left the room, the jury members were extended exemption from jury service for life.
Prosecution barrister Rosemary Walsh KC then confirmed that victim impact statements would be prepared ahead of sentencing.
The judge said a custodial sentence was inevitable, stating it would be “lengthy”.
Donaldson was remanded into custody and showed no emotion as he was led from the court.
There will be a review hearing on September 11 before a pre-sentencing hearing on September 25 at the same court.
The judge also said Donaldson would be placed on the sex offenders register.
Sinn Féin MP John Finucane has said his thoughts are with the victims following the conviction.
Speaking to media at Parliament Buildings, Stormont, Mr Finucane said: “First and foremost our thoughts are with the victims, I think they deserve huge credit and continued support for the bravery that they have shown in putting themselves forward and stepping forward to give evidence to enter into the criminal justice process, and I think firstly all of our thoughts are with them on a day like today.
“This can’t be easy and they deserve our continued support in the time ahead.”
Ulster Unionist leader Jon Burrows said: “Today a jury has found Jeffrey Donaldson guilty on all charges.
“These are among the gravest crimes imaginable, committed against the most vulnerable by a man who spent his career demanding the public’s trust.
“I want to pay tribute to the brave women who gave evidence against Jeffrey Donaldson about the abuse he inflicted on them.
“Their ordeal has been unimaginable.
“The fact that Donaldson showed no remorse and called his victims liars is reprehensible.”
