Grant Thornton International es el resultado de la unión de las firmas Alexander Grant, lo que hoy conocemos como Grant Thornton LLP (EE.UU.) y Thornton Baker, hoy Grant Thornton U.K. Los orígenes de estas firmas se remontan a los años 1924 y 1873 respectivamente.
Grant Thornton International is a non-practicing, international umbrella entity organised as a private company limited by guarantee incorporated in England and Wales. References to "Grant Thornton" are to the brand under which the Grant Thornton member firms operate and refer to one or more member firms, as the context requires. Grant Thornton International and the member firms are not a worldwide partnership. Services are delivered independently by the member firms, which are not responsible for the services or activities of one another. Grant Thornton International does not provide services to clients.