The combined business will create one of the UK's largest independent travel management companies with global revenues in excess of £125m.
The transaction is a cash/share deal and sees ET Travel's current joint managing directors Ian Patterson and Glen Duckworth join The Appointment Group's (TAG) board as joint chief operating officers.
TAG's joint chairman and CEO John Gianquitto said: "Bringing together the experience and skills of both businesses will create a very exciting and dynamic management team, to drive continued growth on a global basis."
TAG has just celebrated 25 years in business, with offices in London, New York, Los Angeles, Melbourne and Sydney, and operates in the corporate, touring, events and leisure travel sectors.
ET Travel has been operating in the UK and European corporate and touring travel sectors over the past 18 years with offices in London and Manchester.