The 30-year-old, whose parents Jas and Pete run Waring Green Stores on Garden Road in Brighouse, said she is thrilled that the billionaire chose her dessert business to invest in.
"I'm so happy," Harpreet told the Courier.
"I can't quite believe it. I'm Lord Sugar's business partner - not many people get to say that."
After battling through weeks of challenges, millions of viewers saw Harpreet win Lord Sugar's backing for her business plan to expand and rebrand her dessert business on Thursday night.
What was Barni's will now be known as Oh So Yum, with dessert parlours already open in Huddersfield and White Rose Shopping Centre in Leeds and an online service that delivers nationwide.
Harpreet said she is delighted that Lord Sugar believes that Oh So Yum is going to be the number one dessert business.
"My friends and family are just so, so proud," she added. "They've seen my journey over the last 10 years and how hard I've worked form a young age, just getting my head down."
Harpreet is planning to open more stores and is currently on the lookout for potential premises.
She is also busy with the online ordering service, which offers desserts that can be delivered nationwide.
Her advice for others looking to start their own business is to "believe in yourself and not compare yourself to others".
"Don't wait until something is perfect," she added. "Get started and you will learn along the way."
Harpreet celebrated her win on Thursday night with a viewing party of The Apprentice final with her family and friends at Jeremy's at the Boathouse in Brighouse.
The past few days have been a whirlwind of interviews for the businesswoman, with appearances on national TV and radio shows including ITV's This Morning and with Vernon Kaye on BBC Radio 2 where she met global superstar Michael Bublé.
Harpreet has wanted to appear on The Apprentice since watching the show as a child.
She said watching and assisting her mum and dad in the shop is what helped instil her strong work ethic.
She went to Hipperholme and Lightcliffe High School and Huddersfield New College before starting to study for a degree at Leeds University.
Because she was keen to get her career started, she began working or Barclays at 19, and finished her degree via The Open University.
She worked her way up to become manager of a branch of HSBC before teaming up with her sister, Gurvinder, to open their first dessert parlour in Huddersfield.
Read about the Halifax baker who made an incredible cake for Apprentice winner Harpreet's viewing party HERE