IEC was established in 1922 with the objective to construct the Bangkok-Aranyaprathet Railway, for the first time ever connecting Thailand to the Cambodian border. This project also marked the first time in Thai history that Caterpillar tractors were introduced to the construction industry.

IEC later registered as a Thai national company in 1953 with a registered capital of Baht 10 million.

In 1965, IEC was appointed as a "Royal Appointment” company.

In 1983, Siam Cement PCL foresaw the potential company growth for IEC, invested and took full control of IEC operations; IEC accordingly became an affiliate of the Siam Cement Group.

In 1990, Siam Cement changed its investment policy, prompting IEC’s management to invest in itself. Joined by a group of additional investors IEC’s management increased the registered capital to THB 120 million.

In 1992, the company was listed in the Communication Sector of the Thai Stock Exchange, and a year later became a public limited company. The IEC has increased its capital continuously, today having a registered capital of THB 2,200 million and a paid-up capital of THB 1,749.23 million (figures as at 31 December 2007).