Converium - which confirmed earlier this year that it was looking to sell its run-off units - said it would sell its operations to Berkshire Hathaway's National Indemnity for a total consideration of $95mn cash and $200mn debt.
Upon the closing of the sale - which is subject to regulatory approval - National Indemnity will assume all of Converium North America's $1.06bn reinsurance liabilities.
Converium estimates the sale will result in a decrease in shareholders' equity of $135mn.
Inga Beale, Converium's chief executive, said: "With this transaction we have successfully delivered on our promise to achieve finality regarding Converium's US operations through a clean-cut sale. We can now fully concentrate on building Converium's future, with our business strategy focused on markets outside the US."
In July, Standard & Poor's placed the reinsurer on a "positive outlook" - a precursor to a possible upgrade from the current BBB+ - and indicated that the resolution of its US liabilities would be a key factor, together with the "successful conclusion of regulatory investigations".
Shares in Converium - which have performed strongly this year - were up 0.6 percent in morning trading at SFr 16.05.