John Thain figured seven months ago that he was just one rung down the corporate ladder from becoming chief executive of the largest consumer bank in the U.S. Now, he is trying to climb back from the professional disaster that followed.

In an effort to restore his sullied reputation, the 53-year-old Mr. Thain is striking back at Bank of America Corp. He claims the bank lied about its role in the giant bonuses and losses at Merrill Lynch & Co. that cost Mr. Thain his job in January, after Bank of America bought the troubled...