Ms Foster has campaigned for justice for survivors of institutional child sexual abuse for many years. Two of her daughters were sexually abused by a Catholic priest, one who has since died.
"Here, we have, today in our court, in Victoria, the Supreme Court, saying - we believe the victim."
Ms Foster said it sent a positive message to victims and their families about the justice system.
"It worked the first time and now it's worked the second time. I'm so glad it was not overturned after everything," she said.
Other survivors who had been waiting outside rejoiced when they heard the verdict.
One man, with a placard saying 'Justice for witness J' said it was "one of the greatest moments".
"As survivors, we are now also being heard, believed and we have now... What can we say? It is a glorious day for us as survivors everywhere. It's just wonderful," he said.
Abuse survivor Stephen Woods was in the courtroom for the verdict – and said he nearly fell off his seat.
Mr Woods endured abuse as a child in Ballarat - which has a long history of child sexual abuse by Catholic clergymen.
He said he texted friends and family in the regional city to let them know.
“Pell was so critical in so much of the cover-up in the Ballarat diocese,” he said.
“It is amazing to see this person, who has so much celebrity, so much money, so much power… Now he has been found to be exposed as a paedophile himself.”
Pell supporter shouted down
One supporter of Pell was shouted down when she tried to say the cardinal was innocent, comparing the case to Lindy Chamberlain, who was found guilty of killing her baby Azaria before being later cleared.
"I can't see any evidence that he's done what he's done," said Karen, who said she was not a churchgoer.
"You are picking on him because he's a priest," she told a woman talking over her who called her evil.
"It's going to be like Lindy Chamberlain - in 20 years' time they're going to find out he did not do anything."
Pell's complainant 'relieved'
The lawyer for the complainant in the case against George Pell, Vivian Waller, read out a statement on behalf of her client.
In the statement, he told of how the four year process had taken a toll on his mental and physical health.
"The journey has taken me to places that, in my darkest moments, I feared I would not return from," Ms Waller read.
"I have risked my privacy, my health, my well-being and my family."
The victim, who has remained anonymous throughout the trial said he was '"relieved" by the verdict, and pleased justice had prevailed.
"I am grateful for a legal system that everyone can believe in, where everybody is equal before the law, and nobody is above the law."
He said he is now ready to move on, and had "started a new chapter" in his life as a father.
On Twitter, the court's decision quickly started trending.
Greens Senator Sarah-Hanson-Young said the decision was a “win for justice”.
“A win for all survivors child sexual abuse and even more importantly for those who tragically never made it,” she said.
Advocacy group CLAN who works with children who grew up in foster care, said "justice in Victoria has prevailed."
Other advocacy groups have also welcomed the news.
"Believing the victim in this case sends a message to so many other victims that what happened to you mattered and will now be more likely to be believed than ever before," a statement by the Blue Knot Foundation said.
"For many survivors a conviction being upheld against a high profile once powerful perpetrator underlines faith in the justice process and the possibility of speaking out."
Human Rights campaigner and actor Magda Szubanski took to Twitter to praise the the Court of Appeal, and send her love to the complainant.
Stripped of Honours
Prime Minister Scott Morrison accepted the decision of the three Court of Appeal judges and said it "must be respected."
“The courts have done their job. They've rendered their verdict," he said.
He added that Pell will be likely stripped of his Order of Australia - an honour he received in 2005 for his services to the Catholic Church in Australia.
Mr Morrison urged survivors to reach out to those around them and said his "sympathies are with victims of child sexual abuse not just today but every day".
Those seeking information or support relating to child sexual assault can contact Bravehearts on 1800 272 831 or Blue Knot on 1300 657 380. Lifeline is available 24 hours a day on 13 11 14.