He started the company in 2004 after seeing a need for high-quality baked goods in New Zealand while working as the head chef and owner of Auckland restaurant Prime Bistro.
Loaf now employs 50 people and sells specialty artisan breads, slices and cakes throughout the country.
"Don't ever tell me I can't do something," Armstrong said. "I am where I am out of grit, determination and hard work."
Other business leaders named in this year's shortlist include Steve Gianoutsos, the founder of Mojo Coffee, and Georgie Falloon, the woman behind Willow Shoes.
Willow Shoes has established a niche market segment in New Zealand offering shoes to women with feet size 10+.
My Food Bag's Cecilia Robinson, ClearPoint's Phil Pietersen and Carnival Labs' chief Guy Horrocks are also in the running for the title.
Jon Hooper, director of the awards programme, said about 30 to 40 applications had been received this year and the shortlist reflected a broad cross-section of New Zealand industries.
"A lot of these businesses have achieved double-digit growth over the past three or four years. They've also been growing employee numbers which is very important in the current climate."
The Ernst and Young Entrepreneur of the Year Awards are held in more than 140 cities and about 50 countries every year.
As New Zealand's 2012 winner, Heatley headed to Monaco two months ago to represent the country at the World Entrepreneur of the Year awards.
The high-profile entrepreneur, rich lister, aviator and competitive amateur golfer won his spot at the event after beating a field of 16 finalists in the local competition last October.
The Kiwi programme was launched in 1997 to honour the contribution entrepreneurs make to the business community and economy.
This year's awards will be announced at the Langham Hotel in Auckland on October 17.
*An earlier version of this story incorrectly named John Plato as being from ClearPoint. ClearPoint's managing director is Phil Pietersen. John Plato, who is also a finalist for the Entrepreneur of the Year Awards, is managing director of Plato Design Agency.