John Brown, 60, was acquitted of five counts of indecent assault against two girls under the age of 13 and 16 at several locations in Northern Ireland and England during the 1970s.
Brown, of Bracknell, Berkshire, had denied all of the claims or that his 62-year-old sister helped him to cover up the allegations.
The All Kinds Of Everything singer kept her eyes closed and then cried as the last verdict was delivered following a total of 11 hours and 54 minutes of deliberations at Harrow Crown Court.
Later she hugged her brother and other members of their family who were in court.
Ms Scallon said she could not comment on the outcome today because of ongoing defamation proceedings over claims she made in a 2011 television interview about the complaints against her brother.
Later giving a statement on the steps of the courthouse, Brown said that both he and his sister had been put on trial by the prosecution.
And he claimed that the aim of the allegations had been to "derail" her 2011 presidential election campaign.
Flanked by his wife Patricia, his sister and her husband Damien, he also expressed his gratitude to the judge and the jury and praised the press for "respecting the integrity of my family" during the trial.
"We are here today because of the initial reporting of this during my sister's campaign in the presidential elections of Ireland in 2011," he added.
"The prosecution have put both myself and my sister on trial. Not only her but our beliefs, our integrity and our faith.
"The jury have delivered their verdict of no cover up. There is nothing to cover up - the accusations are unfounded.
"I came here an innocent man, I leave here an innocent man."
He paused and cried as he thanked his wife and family for "their support in a horrific three years through many challenges".
"Judge (Graham) Arran said I am a person of good character and what sustained me was my faith in God that through this darkness there was light."
Brown was first acquitted by the jury of six men and six women before the lunch break on the charges relating to the girl under the age of 13.
The abuse was alleged to have happened in London and in a seaside town in the south west of England when the girl was as young as between five and seven years old.
Now in her 40s, the woman claimed that on the first occasion Brown had got on top of her, put his hands in her underwear and thrust at her as if they were having sex.
She alleged that he had abused her again in a town she thought could be Torquay in Devon when she was between eight and nine.
Brown was accused of asking her for a "wee hug", rubbing his body against her and pushing her against a wall.
After further deliberation the jury also cleared him of claims that he indecently assaulted a girl under the age of 16 in Northern Ireland and Romford in Essex.
It was claimed that the girl was aged 10 or 11 at the time. Now in her 50s, she said that Brown had fondled her while she was sleeping.
She also alleged that on another occasion he touched her privates and leg on the outside of her pyjamas.
Prosecutor Claire Howell had told the jury that Brown and his sister put on a "slick presentation" during the three-week trial.
But Martyn Bowyer, for the defence, described the prosecution's case as "fuzzy" on the details and said his client had been "consistent throughout".
And he also asked the jury not to be influenced by recent high-profile child abuse scandals.
Ms Scallon first achieved fame after winning the Eurovision Song Contest in 1970 with All Kinds Of Everything.
Born in London to a Northern Irish family, she went into politics in 1997, served as an MEP for Connacht-Ulster and twice stood as an independent candidate at presidential elections in the Republic.