Icahn says in a letter to Trump that he is stepping down to prevent "partisan bickering" about an unofficial role that Democrats suggested could benefit him financially.
Trump lost a pair of business advisory councils on Wednesday over his inability to condemn the role white supremacists played in violence last weekend in Charlottesville, Virginia.
Icahn says in the letter that he never had access to nonpublic information or profited from his position and that he believes there was no conflict of interest. He says that he limited his input to broad matters of policy involving the oil refining industry. Icahn controls a sizable stake in refiner CVR Energy.