The SGML Users' Group came into existence through the initiative of several specialists in text and graphics processing who realized the important contribution that standards can make to the exchange and multiple uses of computer-based information.

The idea of a Users' Group was proposed by Joan Smith at the Markup Conference held in Oxford in April 1984. Joan felt that those who were embarking on the use of SGML would benefit from having a forum in which information could be interchanged. The idea was taken up and it could be said that Bill Tunnicliffe of the Graphic Communications Association (GCA) and Joan Smith became co-founders of the SGML Users' Group.

Three meetings were held in the UK (December 1984, February 1985, and May 1985) prior to the inaugural general meeting held in conjunction with the Markup Conference in June 1985, in Heidelberg. The first draft of the consitution reflected the organizational plans agreed by those present at that inaugural general meeting.

The Group's status as a non-profit organization became official when its application was approved by the Charities Commission of England and Wales in October of 1988 (registration number 800183). The constitution of the Group provided for two levels of membership: individual and corporate, and also allowed the formation of chapters.

Pamela Gennusa took over as president of the group from Joan Smith in 1990. In December of 1996, the Group changed its name to the International SGML Users' Group (ISUG) and filed a revised constitution with the Charities Commission adding a new member class, Chapter. There are two classes of Chapter Membership: Affiliated, a separately constituted body; and Subsidiary, existing as part of the ISUG.

James Mason took over as president from Pamela Gennusa in 1999.