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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Samantha Cameron, the wife of former Prime Minister David Cameron, is launching a new fashion label.