Kent County Council (KCC) has been told it was "unlawful" to prevent a humanist from joining its religious education committee.
A High Court judgment on 26 May found in favour of Steve Bowen, Chair of Kent Humanists.
In his judgment, Mr Justice Constable said it was "clearly discriminatory" to block him from being a full member of Group A of KCC's Standing Advisory Council on Religious Education (SACRE).
Schools have been required to include some teaching of non-religious beliefs in RE since 2015 but the syllabus is set locally, not nationally, by SACREs.
Membership of SACREs is divided into different groups - group A for representatives of the principal religious beliefs in the area, other than the Church of England; group B for the Church of England; group C for teacher representatives; and group D for local authority representatives.
Mr Bowen applied to be a member of Group A in 2021 but KCC rejected his application, claiming that to admit him would be unlawful.
He was supported in his legal challenge against that decision by Humanists UK, who said the implications of the High Court's judgment would be "far-reaching".
Mr Bowen said, "I always knew that it was logical for it to be possible to appoint a humanist to a SACRE in a world where the RE curriculum now covers non-religious worldviews such as mine, as well as religious ones."
