The company, based in Bexhill, East Sussex, said a "large proportion" of its 1,500-strong workforce held shares alongside management and would be "rewarded for their role in the success of the business to date" after the stake sale.
It is believed that more than 80% of employees are shareholders following a management buyout in 2009.
Hastings Insurance Group - which has brands including motor insurer Hastings Direct, People's Choice, Insure and Renew - said the team that led the buyout will retain a 50% stake in the business, while existing management led by chief executive Gary Hoffman will also remain invested in the group.
It is thought that chairman Neil Utley will land a fortune worth tens of millions of pounds after selling part of his stake.
Hastings declined to say how much Goldman Sachs is investing in the group through its m erchant banking division , but said it was a mixture of cash and further debt financing.
Mr Hoffman, who joined Hastings as chief executive last year, said the deal " is a strong tribute to all the hard work that everyone in the Hastings team has put in so far".
The group's boss led the turnaround of Northern Rock during its period in government ownership after the bank's collapse in 2007.
Hastings has 1.3 million customers after increasing the number of policyholders on its books by 17% in its last financial year and has aims to insure one in 10 UK customers by the end of the decade.
It made underlying earnings of £83.3 million in the year to the end of June.