Fischer’s career began as a computer entrepreneur when he created his first high-tech startup company in 1973. He went on to became majority owner of RSA Data Security, which founded VeriSign. He founded Fischer International Systems Corporation and Fischer International Identity, LLC, corporate software providers to the Global 2000, and Fischer presently serves as chairman of both companies. Since 1981, he has served as co- owner, with Stanley Druckenmiller, of Duquesne Capital Management until Druckenmiller’s retirement in 2010.

He was a member of official committees that set U.S. standards for computer security and electronic commerce. He has addressed the U.S. Congress, by invitation, on several topics, including digital signature standards, proposed FBI digital telephony legislation and global U.S. competitiveness. From 1995 through 1999, Fischer was a member of the Computer Systems Security and Privacy Advisory Board established by the Computer Security Act of 1987 to advise the president and report to Congress on issues regarding United States computer security. Fischer's seminal paper “Electronic Document Authorization,” as well its companion paper “WorkFlow 2020,” laid out many of the innovations, which have since been incorporated into widely-used commercial products such as Java. Fischer holds numerous U.S. and international patents and is a lifetime member of the Association of Former Intelligence Officers.

In addition to his business interests, Fischer has been an active philanthropist on issues concerning the environment, resources, health and freedom. Fischer serves as a director of The Jane Goodall Institute and the EastWest Institute, and is on the advisory boards of the Electronic Privacy Information Center (EPIC), the Amazon Conservation Team and the Sylvia Earle Foundation. He holds Mathematics degrees, as well as an honorary doctorate from West Virginia University.