More than 99.5 per cent of votes cast by Old Mutual were in favour of floating the insurer, bringing 300 windfall shares worth more than pounds 400 to each member. Only 0.3 per cent of voters were opposed.
The vote has been portrayed as a moment of "economic empowerment" in South Africa, where the value of the windfall equates to more than a year's salary for a large proportion of the members.
Mike Levett, Old Mutual's chairman and chief executive, said: "This is a milestone in the history of Old Mutual. We are delighted that so many members took part and voted `Yes'.
"We can now move forward with the implementation of our plans for the benefit of members, Old Mutual and Southern African."
The insurer will list in London as well as Johannesburg. Shares in the insurer are expected to begin trading towards the end of June with an estimated share price of 11 to 14 rand, or around pounds 1.25.
The result of the ballot, announced at a special general meeting held in Cape Town, South Africa, was the climax of more than 18 months of preparation.
The intention to float the insurer - by far the largest insurer in South Africa - was first made public in August 1997.
It will benefit not only South African and British policyholders, but also members in Bermuda, Malawi, Namibia and Zimbabwe - subject to the approval of the courts in each country.
More than 900 employees of Capel Cure Sharp, the private client broker, are also set to receive 300 shares each.
The insurer has run operations in the UK since the early part of the century, owning Old Mutual International and Old Mutual Asset Management in the UK.
But it has made few significant inroads into the UK life insurance market.
Some observers have been critical of the insurer's record on lapsing life insurance policies - a key factor in judging the quality of financial advice provided by its sales people.