On Sunday, the Duchess wore Wickstead's aquamarine pleated dress, with a matching Jane Taylor hat and a green clutch and heels by Emmy London, as she stepped off an RNZAF jet in Dunedin.
She wore it to a church service.
It was the first time she had worn a local designer on her trip.
Catherine has previously worn several bespoke pieces from the designer, including a pastel pink version of the aquamarine dress in 2012.
Wickstead said her own visit to New Zealand was coincidental.
A new mother, she brought her daughter Mercedes Amalia, 1, to see her 90-year-old grandmother.
Wickstead praised the Duchess for being a role model for young girls.
"She's so lovely and what she does for British fashion and young girls, she's made them think that it's great to dress up again and be elegant and groomed.
"I think it's so fresh for the world we live in now because it is an old-world version of dressing."
Famous clients such as Catherine and the British Prime Minister's wife, Samantha Cameron, have put her designs on the global stage, but she gives credit to her Kiwi upbringing for her thriving brand.
She grew up in Auckland, but moved to Milan when she was 14 after her mother - also a designer - married an Italian.
After studying design and marketing, Wickstead started her made-to-order business out of her London flat.
