The top spot came after three successive years of netting silver gilt.
Yorkshire in Bloom judges praised the knowledge and commitment of staff and the army of volunteers as well as good display borders and signs, neat car park and clean café and toilets. The 48ha park welcomes 200,000 visitors a year and has won a Green Flag for eight years.
The category Oakwell Hall competed in was for country houses, estates, parks and gardens and councillor Jean Calvert, cabinet member for wellbeing and communities, said it rewarded huge amounts of work by rangers, staff and volunteers.
"This helps create a feelgood factor for everyone who works in the park and everyone who visits. I am extremely pleased that the park has been honoured with this award."
Other gold winners included Burton Agnes Hall, East Park Estate, Elsecar Park, Homestead Park, Lister Park, Pannett Park, Parcevall Hall Gardens, Sheffield Botanical Gardens, Stewart's Burnby Hall Gardens and Museum Trust and Thorp Perrow Arboretum Gold.
Silver winners were Breezy Knees Gardens, Cannon Hall, Museum Gardens York and Spa Gardens, Ripon; and silver went to Sutton Park.