Supporters are being asked to bring black balloons to the demonstration as anger grows over how Fiona's father walked free from court this week despite being found guilty of raping her for 10 years.
Ms Doyle is also seeking an urgent meeting with Taoiseach Enda Kenny while the fallout from the case continues.
Patrick O'Brien from Bray, Co Wicklow, was sentenced to 12 years in prison with nine years suspended and is currently out on bail pending an appeal of the three-year prison term.
He pleaded guilty to repeatedly raping his daughter over a period of 10 years from the eve of her First Communion.
Thousands of supporters have already signed a Facebook page -- JusticeForFionaDoyle -- and a blitz of protest emails to Justice Minister Alan Shatter is also underway.
Twitter users too are also calling for an end to lenient sentences for sex abusers.
Organisers of Saturday's rally are hoping it will be as well supported as last weekend's anti-abortion protest at the gates of the Dail, which was attended by 25,000 people.
The Taoiseach yesterday paid tribute to Fiona Doyle's courage but was vague about the prospect of the Government bringing in mandatory sentences for rapists.
"I admire the courage of Fiona Doyle in doing what she did," he said.
"I would like to believe that others who have or are subject to rape or incest or crimes of this horrific nature would not lose courage in coming forward to say their piece."
The question of mandatory sentencing for rapists, he stressed, was a "matter for the Government to reflect upon".
Today Fiona Neary of the Rape Crisis Network said they did not see mandatory sentences as a solution but wanted sentencing guidelines.
They also called for an end to any granting of bail once a sentence was passed other than in the most extreme circumstance.
Calling for guidelines, she said: "We really feel this is the way to start approaching sentencing." It would also mean that "victims will feel that their voices are being heard".
The Network is writing to the Justice Minister calling for measures to ensure consistent sentencing of convicted sex offenders.
Children's charity Cari has expressed fears that the handling of Fiona Doyle's case could be "seriously damaging to public confidence in the legal system".
Chief executive Mary Flaherty said Ms Doyle had been "revictimised" by getting caught up in a dispute between the presiding judge, Mr Justice Paul Carney, and the Court of Criminal Appeal.