Developers Mynydd y Gwynt Ltd hoped to build 27, 128-metre turbines beside the A44, about 10 kilometres east of Ponterwyd, and last year won the backing of a planning inspector after a public inquiry.
But the then energy and climate change secretary, Amber Rudd, rejected the inspector's recommendation and refused planning permission in November last year.
The site was close to the Elenydd Mallaen Special Protection Area and she was was unconvinced that the development would pose no real threat to the local population of protected red kites.
The developers said the risk to the birds would be "nil" and argued that Rudd had misunderstood the threat and taken no account of measures it would take to protect the birds.
But yesterday the company's legal challenge to Rudd's decision was rejected by High Court judge Mr Justice Hickinbottom.
Given the "important unknowns" in the case - including doubts about the number of red kites that might stray from the special protection area to forage on the site of the proposed wind farm - she was entitled to conclude that consent should be refused", he said.
The judicial review challenge was dismissed.
R on the Application of Mynydd y Gwynt Limited v Secretary of State for Business, Energy and Industrial Strategy. Case Number: CO/6580/2015