McColl joined the precursor to NationsBank in 1959 and quickly progressed through the company. As CEO, he built NationsBank into the third largest bank in the country by 1995. He did so through the accumulation of close to 50 acquisitions. Between 1995 and 1998, the value of NationsBank stock tripled. In 1998, McColl oversaw the merger of NationsBank and the Bank of America which resulted in the creation of the second largest bank in the United States. McColl presided over the merger of the entities and its further expansion.