Tokyo, Nov. 22 -- Nissan Motor Co. fired Carlos Ghosn as chairman Thursday, curtailing the powerful executive's nearly two decade long reign at the Japanese automaker after his arrest for alleged financial improprieties.

In an hours-long meeting, the company's board of directors voted unanimously to dismiss Ghosn as chairman and as a representative director, Nissan said in a statement. It said its own internal investigation, prompted by a whistleblower, found serious misconduct including under-reporting of his income and misuse of company assets.

It was a stunning downfall for one of the biggest figures in the auto industry, a man who helped drive turnarounds at both France's Renault SA and at Nissan and then managed an alliance between...