Martinborough and Featherston already have parks and Greytown residents had requested their own.
"We've got a lot of dog owners in Wairarapa that need places to bring them and socialise," said Mrs Staples.
Council dog ranger Andrew McEwan said it had been a long time coming.
"We've been wanting to get a third park for ages.
"It's not just a dog park, it's a great place to meet people, they've got a common interest."
He said the parks were also a safe place for dogs to play with hardly any issues of aggressive dog behaviour.
Featherston ward councillor Colin Olds said he expected it would become a popular place, like the other two have.
"These little parks become quite social areas where the owners chew the fat and let their dogs run free.
"It's another valuable asset for the South Wairarapa community, all three towns have one now."
The park is on the old railway shed land on the corners of Cotter St and Pierce St.
Residents, Lions members, community board members and South Wairarapa councillors Margaret Craig, David Montgomerie, Solitaire Robertson and her dog Bella, were also there to celebrate.
The first Arbor Day planting in New Zealand was held in Greytown on July 3, 1890.
