Entrepreneur Sara Davies is the founder of global company Crafter's Companion, which she set up in her bedroom and turns over £34 million a year. At 35, she will be the youngest ever Dragon.
Her business, specialising in craft tools, employs more than 190 staff in the UK, the US and Europe.
She said she was "absolutely delighted" to join the other Dragons.
"I've always been very passionate about investing time in and sharing my expertise with other entrepreneurs and hopefully I'll be able to help some of the contestants to really take their businesses to the next level," she said.
"I've been a fan of the show since it started, I was even invited to pitch on the show 13 years ago so it feels like I've come a full circle.
"It wasn't all that long ago when I was in the position of the contestants so I really feel like I will be able to relate to their stories and their journeys so far."
Davies, who set up her business from her bedroom while at university, will join Deborah Meaden, Peter Jones, Tej Lalvani and Touker Suleyman in the Den.
BBC Two controller Patrick Holland said: "Sara is a formidable business woman and I can't wait to see her start in the Den."
The next series of Dragons' Den is due to air later this summer.