The commission, in a 7-1 vote, said historical research and theological investigation "excludes the possibility" of allowing women to serve as deacons at this time but recommended further study of the issue.
Discussions about the possibility of women deacons, who are ordained and can assist with Church services but cannot celebrate Mass, have convulsed the 1.4 billion-member Church for the past decade.
Catholic deacons can baptise people, witness marriages and preside at funerals, among other duties. In some areas of the world they can also lead parishes in the absence of a priest, but a priest must still celebrate the Mass.
The role, for centuries considered only a stepping stone to the priesthood, was reenvisioned as a permanent post for married Catholic men after a series of reforms by the Church in the 1960s.
Some women have said they believe God is asking them to take on the post, which is understood by the Church as a role of service.
The panel, led by a cardinal and a priest from the Vatican's top doctrinal office, included men and women church scholars. They said in the report released on Thursday that their assessment against women deacons was strong, but "does not as of today allow a definitive judgement to be formulated".
The late Pope Francis opened the conversation, after a request in 2016 from the Rome-based umbrella group representing the world's Catholic sisters and nuns.
Francis instituted two commissions to study the matter, which deliberated in secrecy. Thursday's report is the first time that the results of the discussions have been made public.
The new report comes in a letter sent to Pope Leo by Italian Cardinal Giuseppe Petrocchi, who led the second commission created by Francis. The letter is dated September 18 but was released by the Vatican on Thursday.
Leo, a relative unknown on the global stage before his election in May, is not known to have commented on the issue of women deacons.
