The health club chief, who was one of the original team of business experts when the programme launched in 2005, will step down after the upcoming 12th series, which begins later this month.
The 65-year-old said he was leaving the programme - in which the "dragons" are presented with business ideas by budding entrepreneurs before potentially offering investments -"due to other business commitments".
He said: "I have had the time of my life as a dragon. I have made numerous investments and taken part in a landmark TV programme that has promoted entrepreneurship to a generation of Britons.
"However, after the 2014 recordings I do not plan to make any further investments on the programme so I thought it fair to ask producers to offer my seat to somebody else.
"There are only so many times I can say 'I'm out'. The series that is about to be transmitted is my final season and I'm delighted it is full of exciting, high-quality pitches. I have made a number of investments."
His departure leaves only telecoms magnate Peter Jones from the dragons' starting line-up. By the most recent series Bannatyne, whose first notable business success came after he bought an ice cream van for £450 and later sold the business for £28,000, has invested almost £2 million on the show.
Born in Clydebank, he built up his fortune with nursing homes and nurseries before founding his health club and spa chain in 1997.
He was estimated to be worth £430m by the Sunday Times Rich List in 2011. He went through a costly divorce from second wife Joanne McCue later that year, leading to speculation in early 2012 that uncertainty over his finances meant he would quit Dragons' Den then.
He dropped off the rich list in 2013, after becoming locked in a battle to pay off £122m which he borrowed from the collapsed Anglo Irish Bank.
But earlier this year, it emerged Bannatyne had agreed a £92m deal to sell and lease back 39 of his health clubs, allowing him to clear his loans. He returned to the latest edition of the rich list, with an estimated worth of £175m.
He was awarded the OBE in 2004 for services to business and charity. During a visit to an Easterhouse charity in 2008, he said he wanted to give away his entire fortune before he died. He is also known for his involvement with Comic Relief and Unicef.
In recent years, he has made controversial statements on Twitter, using the micro-blogging site to call for the reintroduction of hanging in 2011. Earlier that year, he had offered a £50,000 reward on Twitter to anyone who broke the arm of a blackmailer who had threatened his daughter.
After backing the Union ahead of the independence referendum, he said he had been subjected to attacks from "racists".
Mark Linsey, the BBC's controller for entertainment commissioning, said: "Duncan has been the most formidable dragon and we are going to miss him enormously. He has inspired many entrepreneurs to come on the show and helped make Dragons' Den a huge success for BBC2. His seat is going to be a difficult one to fill."
Bannatyne is expected to remain on screen until next year.
l Meanwhile, the BBC Trust has ordered a review into how the corporation pays its stars but says it will not publish details of "individual talent deals".
The review, the first to look at how presenters and on-air talent are paid since 2008, will examine if the policy of reducing costs is "sustainable in the future".