Shepway District Council had granted consent for the holiday village at Little Densole Farm, Densole, in the heart of the Kent Downs area of outstanding natural beauty (AONB), in defiance of its own planning officer's advice.
David and Lucy Westgarth had wanted to build 12 holiday lodges, a reception building, a fishing lake, a car park, tennis courts, a children's play area and a putting green.
As well as being in the AONB, Little Densole Farm is in a locally designated special landscape area.
A planning officer's report recommended that permission be refused - but the council's planning committee went its own way in February last year.
Committee members decided, by a majority of seven votes to two, that the project would "conserve and preserve the scenic beauty" of the area.
Describing the location as "suitable", councillors pointed to the "significant employment and tourism benefits" of the development.
Local resident Timothy Steer spearheaded a judicial review challenge to the council's decision.
The judge found that it had not been proved that councillors failed to take proper account of national planning policies.
It had also not been shown that the committee reached an irrational conclusion that the project would cause "no harm" to the AONB.
But, overturning the permission, she ruled that the committee had given inadequate reasons for its decision.
Having rejected the planning officers’ views, councillors could not rely on his report as supporting their conclusions, she said.
And the minutes of the meeting were by themselves insufficient to dispel the "substantial doubt" over the committee's decision, she added.
"The defect in reasons goes to the heart of the justification for the planning permission and undermines its validity," she said.
The planning permission was quashed and the council was ordered to pay £22,750 in legal costs.
Earlier this month, the High Court overturned an Essex home approval due to a lack of a "reasoned explanation".
And shortly before Christmas, the Supreme Court ruled that local planning authorities must give reasons for granting planning permission when fairness so requires.
R on the Application of Steer v Shepway District Council. Case Number: CO/3051/2017