Tower has won the right to renew insurance policies sold to ANZ and National Bank customers, following a messy separation between the insurance company and the two banks.
The banks sold Tower's policies to customers until 2008, when their parent company, ANZ, dropped Tower in favour of a competitor.
Since then, the two companies have been fighting for the business of 110,000 customers with motor vehicle, home, contents and travel insurance.
The Court of Appeal ruled on Friday that the insurance book should remain with Tower, allowing it to renew existing policies.
But, it also said Tower should provide protected information to ANZ and National, so that the banks can try to regain their insurance custom with their new partner, Vero.
The bank has moved to reassure customers they won't be disadvantaged by the ruling and their policies are unaffected.
Shares in Tower fell 5 cents to $1.53 on Friday. ANZ shares dropped 55 cents to $27.70.