At the Geological Society's Council meeting on 1 November 1972 it was decided to set up a working party to study the feasibility of maintaining a professional register of geologists. The Society's Council established a 14-strong Working Party on Professional Recognition which first met on 2 January 1973 and reported to Council in March 1974. Their report recognized that professional bodies carried out important functions in regulating the professions, however no existing professional body was deemed an appropriate institution for all geologists to become members. Consequently, the Working Party recommended that a professional body should be established for all geologists.
The Association for the Promotion of an Institution of Professional Geologists, more usually known by its initial letters APIPG, was established by the members of the Working Party, by now acting independently of the Society's Council but with its support. The first meeting of APIPG was a regional meeting held in Plymouth on 3 January 1975. It was followed by a series of eight more regional meetings held in locations around the country. The formal Inaugural Meeting of the Association took place on 24 March 1975 at the Scientific Society's Lecture Theatre in Savile Row, London. At this meeting, a Committee was formally elected to serve for two years with the sole objective of forming an Institution for Professional Geologists. In the event the process took a little longer with the new professional body being created 35 months after the Savile Row meeting. Over that period support from the geological community grew steadily from 620 members in mid-1975 to 963 in mid-1976, and by the end of APIPG's existence there were 1146 members.
By the end of 1977 the Institution of Geologists was fully established in embryonic form. The Institution of Geologists registered as a company limited by guarantee without share capital, a form of organization shared by a number of other professional institutions. It was incorporated in August 1977 with the subscribers being the APIPG Committee. The membership of APIPG voted for the organization to be disbanded and replaced by the Institution of Geologists at a meeting held in the Midland Hotel Birmingham on 24 February 1978.
The highest grade of membership in most professional institutions is termed "Fellow". Initially, IG had only one grade of corporate member (that of Member). By June 1985 however, Council decided to initiate a higher grade of corporate and nominated the former Presidents and Chairmen of Council as six Founding Fellows. A further fourteen members of IG were nominated by this group to form a Founding Fellows "college" of twenty. A Trust Fund was established in 1986 to commemorate the memory of three distinguished geologists who were also Founding Fellows of the Institution and died within a relatively short time of each other. The fund, known as the Distinguished Fellows Memorial Trust, was used to assist young geologists, particularly those in industrial employment, in their professional development by contributing towards travel costs to attend conferences or to gain experience in other appropriate ways.
In 1983, the IG Council decided to enquire of its members what they expected from the Institution in order to establish priorities in planning the development of IG. A questionnaire was sent to the regional groups to ask them to canvas opinion and provide a response to Council. The unanimous answer was that the prime objective should be the acquisition of a Royal Charter which would bestow on the Institution the ability to create the title Chartered Geologist. In January 1984 a committee was established under the chairmanship of Howard Headworth, to investigate how this goal could be achieved. In January 1986 a draft charter was sent to the Privy Council for informal comment. As the document referred to the possibility of a future unification between the IG and the Geological Society, the Privy Council refused to consider the petition as the Geological Society already had its own Royal Charter. Instead they recommended that the petition should be placed on hold until the possibility of any merger between the two organizations was resolved.
The Institution approached the Geological Society to explore a possible merger. A joint Co-operation Committee was established, comprising three senior members of each organization and chaired by Professor Howel Francis as someone seen as neutral by both sides. The first meeting of the joint Co-operation Committee was held in January 1987 and agreed that the unification of the Geological Society and the Institution of Geologists was the proper goal for the two organizations, both in their own interests and that of the geological community in Britain. Negotiations between the IG and GS even included the concept that the new body should have a new name but that was not possible without changing the Society's Royal Charter. In the end, the IG merged with the Society losing some of its identity in the process and with its name disappearing altogether.
With the reunification 259 members of the Institution who had not been Fellows of the Society applied for and were granted fellowship, and some 586 corporate members of the Institution became the first Chartered Geologists even before the reunification process was completed. The total membership of IG at the time of the reunification was 1745, comprising 32 Fellows, 731 Corporate Members, 674 Associate Members, 9 Technician Geologists, 6 Technical Associates, 42 Affiliates and 251 Students.
A vote at IG's AGM on 10 March 1990 at the University of Birmingham saw the demise of IG as a separate organization, and at the beginning of 1991 the Institution of Geologists formally unified with the Geological Society.