After earning his MBA, Purcell joined McKinsey & Co. He quickly climbed through the ranks until 1975 when he was named the youngest-ever managing director of the Chicago office. In 1978 he joined Sears, Roebuck & Co., where he spearheaded the acquisition of Dean Witter in 1981 and directed the creation of the Discover Card in 1985.
Purcell was named chairman and CEO of Dean Witter/Discover in 1986. When Morgan Stanley and Dean Witter merged in 1997, he successfully united two vastly different corporate cultures, ultimately becoming chairman and CEO of Morgan Stanley Dean Witter & Company.
Purcell was also chairman & CEO of NOVUS Credit Card Services. He was a director of Dean Witter InterCapital, Inc.; Dean Witter Realty, Inc.; Dean Witter Reynolds, Inc.; Levelor; Sears, Roebuck & Co.; and the Securities Industry Administration. He was also chairman of several NOVUS and SPS subsidiaries as well as Discover Card Services, Inc.