They will also be joined by Maya Jama as the series host.
Barlow, Dixon, French and David will head into the studio together for the first time this month to record the series which will begin airing on ITV later this year.
Cowell's line-up pulls together his long-time Britain's Got Talent colleague Dixon and former X Factor judge Barlow, as well as comedian French and singer David in their first talent show panel roles.
Dixon said: "When Simon first told me about the format, I couldn’t wait to see it come to life. Now to add being a part of it alongside Gary, Craig, Dawn and Maya is very exciting."
French added: "I’m far too excited to be part of this show, I’ve decided to wear double knickers at all times."
Walk The Line sees soloists, duets and groups battle it out on stage each week as the top acts each episode are then given the choice of cashing out with a smaller money prize, or literally walking the line in the hope of making it through to the next week.
So far, details of what "walking the line" will involve haven't been released, but acts with nerves of steel could go on to win the series jackpot of £500,000.
David said: "Walk The Line is innovative, new and edgy which is why I’m so excited to be working on this show.
"I’m really vibed by the quality of the contestants I’ve seen so far and love that they have the chance to bet on themselves every step of the way."
Barlow, who judged The X Factor from 2011 to 2013, said: "When Simon calls it’s usually with something fairly extraordinary. I’m so excited to be involved in a brand new TV show, and of course my favourite part of Walk The Line is discovering new talent."
Presenter Jama said that it was a dream come true to be hosting one of Cowell's prime time shows.
She said: "This has been a childhood dream of mine. I remember watching shows created by Simon when I was younger, and to be given the opportunity to host one myself… it has definitely been a pinch me moment.
"I’ve been itching to tell everyone about it – expect some first class entertainment and truly incredible singing talent. Walk The Line has been unlike anything I’ve worked on before and I hope everyone has as much fun watching it as we are making it."
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