General Motors Co. will drive away from its U.S.-government-financed restructuring with a final gift in its trunk: a tax break that could be worth as much as $45 billion.

GM, which plans to begin promoting its relisting on the stock exchange to investors this week, wiped out billions of dollars in debt, laid off thousands of employees and jettisoned money-losing brands during its U.S.-funded reorganization last year.

Now...