Employees of car insurers Admiral are set to receive an average windfall of about £37,000 as the company sells a 10% stake.
Staff in Admiral's Cardiff office were 'buzzing' about the sell-off
Admiral, part-owned by its workers, set a price of 275p a share on Thursday, valuing it at £711m (1.04bn euros).
Trading will begin on Tuesday but in unofficial trading, shares in the company rose 3.75% to 285.5p.
Individual windfalls depend on length of service with some staff set to make hundreds of thousands of pounds.
Admiral will have a market valuation of £711m(1.04bn euros) when it floats next week.
The company has 1,100 staff in Cardiff and another 400 in Swansea.
"I am absolutely thrilled with the outcome," chief executive Henry Englehardt said of the share sale.
The decision to float comes five years after Admiral was sold to its management team in a buy-out backed by Barclays Private Equity.
As its largest stakeholder, Barclays Private Equity will sell 15% of the company's shares, while management and employees of Admiral will sell 12%, and Bermuda-based insurer XL Capital will sell 5%.
Admiral was set up about10 years ago and has more than 900,000 customers.