He said that while he accepted the planning inspector's appraisal that the development would cause "considerable harm" to the local landscape – which includes Powis Castle - business-promoting guidance in Wales' key planning document, Planning Policy Wales, outweighed those issues.
Farmer Fraser Jones’ application sought to extend his existing dairy unit with a three-storey parlour building, three cubicle buildings and other associated works to support the expansion of his herd from 300 to 1,000 cows.
The scheme, which attracted local hostility because of its proximity to a primary school and other environmental concerns, was initially refused by Powys County Council, before being the subject of a public inquiry in March this year.
Planning inspector Katie Peerless recommended that the scheme be refused because of the harm it would cause to the local landscape, including the Holy Trinity Church and the terraces of Powis Castle.
She said that while other environmental concerns could be dealt with and although the scheme would have "clear economic benefits" through the creation of around 10 jobs, those benefits were not strong enough to outweigh the other concerns.
"Overall, I conclude that the development would be unacceptably harmful to the setting of the heritage assets at Powis Castle and the Leighton Hall Estate and to the character and appearance of its surroundings and, on balance, contrary to the development plan and national policies that regulate such development," she said.
Overturning the decision, Sargeant said he agreed with most of the inspector’s conclusions, and that the development would cause "considerable harm" to the landscape, but disagreed with her economic appraisal.
He pointed to Planning Policy Wales guidance that calls for a recognition "that there will be occasions when the economic benefits will outweigh social and environmental considerations".
Sargeant said the favour accorded to the scheme for the jobs it would create, the increased milk yield, and the farm-owner's anticipated "seven-figure" investment in the project should have been "far more substantial".
He said: "I disagree with the economic weight the inspector has attached to the economic benefits arising from the proposed development and consider that they, together with the other benefits identified, are such, in this case, as to override the objections to it in relation to the landscape and heritage assets."