The private equity-owned company, which has more than two million customers, is expected to be valued at around £3 billion including debt.
Members of the public will be able to apply for a minimum of £1000 of shares in the company, although customers and staff will be given priority and will also be entitled to one free share for every 20 they acquire.
Saga has already canvassed its customers and found that around 700,000 would be interested in buying shares.
The move will be the biggest shares sell-off since the controversial sale of Royal Mail last October, when more than 700,000 people applied for shares in a flotation that initially valued the delivery firm at £3.3bn.
The flotation will also represent a big pay day for an estimated 6000 current and former employees of Saga and its sister business the AA.
They own about 13% of the business, alongside private equity firms including Charterhouse.
Executive chairman Andrew Goodsell said: "Our customers are at the heart of our brand and I am delighted that they will have an opportunity to become shareholders in the company and to be part of the next stage of our journey."
Saga, which started as an out-of-season holiday provider in 1950, now offers services ranging from cruises and holidays, home and motor insurance, savings and share dealing through to the UK's best-selling Saga Magazine.
Proceeds of around £550 million will be used to reduce debt.