Groups involved in the prison and penal system joined with the Labour Party to attempt to keep the prison in Shankill, Co Dublin open.
Mr McDowell has ordered the closure of the prison because he said it was not suitable for current needs. In its place he intends to open a series of half-way house hostels to help young offenders back into the community.
The castle with 30 acres of prime land on Dublin's southside could make 60 million on the property market.
The rate of repeat offending by young people between 16 and 21 who stay at Shanganagh is only around 30 to 40%, compared to a rate of around 90% for the entire prison system, according to Irish Penal Reform Trust chairperson Valerie Bresnihan.
Claiming that Mr McDowell was in breach of human rights law, Ms Bresnihan vowed to take the issue to EU and UN levels.
“If we put young offenders into a place where they come out worse its just nonsensical,” Ms Bresnihan said.
Prison Officers Association deputy general secretary Eugene Dennehy said there are 319 juveniles in adult prisons, including 88 in Mountjoy. Yet Shanganagh currently holds just 20 of a possible 60 offenders.
“I do believe our prison system does need a half-way house and rehabilitation centre for young people. Yet the only rehab now available in Shanganagh is a mop, a bucket and a brush because every other rehab facility has been withdrawn,” he said.
Labour justice spokesman Joe Costello described the move as the most retrograde decision on penal policy ever made by a Justice Minister.