The broadcaster and businesswoman has been a member of the feared panel for the past two series, and is now co-anchor of the Newstalk Breakfast radio show.
She co-hosts the Today show on RTÉ with Bláthnaid Ní Chofaigh, and runs a publishing company.
Commenting on her decision to quit the popular programme, Ms Casey said other work commitments meant she could not give the same time and energy to the show.
“I enjoy working with the investments I have made during my time in the Den,” said Ms Casey. “I intend to continue to explore new investment opportunities in 2013.
“I am also working on new media projects which will complement my busy schedule. I am absolutely certain this is the right decision for me at this time in my life.”
Larry Bass, CEO of Screentime Shinawil which produces Dragons’ Den, said he was sad to lose Ms Casey from the line-up.
“On behalf of the Dragons and Shinawil, we wish Norah Casey well with her future business and media endeavours,” said Mr Bass. “Norah was a great asset to the show and she will be missed by the team. We are very sorry to see her go.
“We will be announcing the new line-up over the coming week. However, in the meantime we are currently looking for budding entrepreneurs for the next series.”
* Budding entrepreneurs looking to take part in the upcoming series of Dragons’ Den can find details on bankofireland.com/dragons