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.
Ms Scallon said she could not comment on the outcome 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 both he and his sister had been put on trial by the prosecution.
And he claimed 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.