Rod Orrock, who formerly managed the retailer from Australia, will now solely oversee parent company Greenlit Brands' portfolio of retailers.
Orrock said Leonard's expertise and background in online shopping, social media and apparel sourcing was an asset and would be critical for the retailer's growth.
"Linda has been an integral part of the senior management team since she joined Postie in 2015. Her contribution helped the company to turn a profit last year and she has supported strong foundations for sustainable growth," Orrock said.
The retailer had focused its attention on quality product and heavily invested in its online offering in recent years, he said.
"We've kept our eye firmly on value and quality, invested heavily in our online offering, and Linda's strong understanding of our customer will ensure we continue to cater to the Kiwi mum and her family."
Postie Plus was founded on the West Coast by the Dellaca family in 1909. Since then it has grown to a network of 63 stores and employs around 420 people.
Leonard said she was excited about leading the company and that the company would continue to adapt to changing consumer needs.
"As new entrants hit the New Zealand market, it's important that we continue to really listen to our customers and meet their needs better than our global competitors.
"I'm very lucky to work with a world-class team of people with a genuine collaborative culture, and I look forward to the next chapter in Postie's journey."
Postie Plus was bought by Pepkor Limited, a global retailer headquartered in South Africa in 2014, the company later became part of the Steinhoff International Group and the South East Asian division was last year renamed to Greenlit Brands.