The Sun newspaper will join the legal action over the Parole Board's decision to release black cab rapist John Worboys.
Judges sitting at the High Court on Wednesday gave the go-ahead for a judicial review brought by two of the sex-attacker's victims and Mayor of London Sadiq Khan.
Sir Brian Leveson and Mr Justice Garnham also gave permission to The Sun's proprietor, News Group Newspapers Ltd, to challenge the Parole Board's refusal to publish its decision.
The Sun's lawyers say the refusal was "unlawful" and argue the rule which prevents the Parole Board from releasing the decision, or any reasons for it, breaches the newspaper's right to freedom of expression.
Gavin Millar QC, representing News Group, added: "This case raises questions of profound public importance concerning the application of the open justice principle and rights to information in respect of judicial decisions made by the Parole Board in its capacity as a court."
A spokesman for The Sun said: "We're pleased that, alongside Worboys' victims and the Mayor of London, we can pursue our challenge to a full Judicial Review.
"There is a clear case to be made for greater transparency and we look forward to making it again next month.
"The public interest is not served by the current wall of secrecy surrounding the reasons for Mr Worboys' release."
The full hearing will be held on March 13 and 14.