She is calling the brand Cefinn - taking inspiration from the initials of her four children Elwen, Florence, Ivan and Nancy.
Mrs Cameron said she wanted to design "an urban uniform for busy women" and that she felt there was a "gap in the market".
Her husband stood down in July after the EU referendum.
She was lauded for her sartorial choices during his tenure as prime minister and regularly championed the British fashion industry.
Items from the 40-piece ready-to-wear collection, launching for spring/summer 2017, will retail at between Â£100 and Â£300.
Mrs Cameron said: "I wanted to create an urban uniform for busy women who love fashion.
"I felt there was a gap in the market for a designer British brand at a contemporary price point offering a capsule wardrobe that takes you from day to evening."
A publicity picture shows her in a sleeveless black outfit with scarlet piping at the shoulders, taken from the collection.
Mrs Cameron, who has a consultancy role at luxury leather goods makers Smythson, where she was previously creative director, was named one of the best-dressed women in the world by Vanity Fair last year.
She is also a British Fashion Council ambassador.
She told Vogue she had "spent a lot of time trying stuff on friends", and added: "I felt that there was a lot of American and French brands out there that fit that bracket of designer contemporary with the right price point and the right styling, but there aren't that many British brands which fill that space."
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The woman contacted security staff after her waters broke at the Intu Lakeside Shopping Centre in Essex.
Although an ambulance was called and arrived quickly, the baby girl was delivered before they got to the scene on Thursday evening.
Paul Lancaster, regional manager of Intu, said the woman had been in "distress" but was now "doing well".
Staff at Primark provided towels for the woman on the second floor of the shopping complex.
She was screened off as she gave birth to her daughter, whose name is understood to be Deborah.
"In 23 years we've never had a birth at the site," said Mr Lancaster. "Plenty of ladies have broken water and gone off to hospital and no doubt a couple of babies have been conceived here.
"It all happened rather quickly before the ambulance could get there. They responded really quickly.
"We didn't think it was immediately going to happen but the baby was born on the spot."
Samantha Cameron, the wife of former Prime Minister David Cameron, is launching a new fashion label.
[NEXT_CONCEPT]
A shopper ended up giving birth outside a Primark store after she suddenly went into labour.