Thorneycroft-Smith is charged with developing the company's market share across marketing as well as other sectors.
Thorneycroft-Smith said: "The way forward is to provide business intelligence and build stronger businesses for clients. Eclipse's values of turning data into profits and its knowledge of using customer information from CRM, recalls or crisis management programmes are well recognised by its household named clients."
In addition to his new role, Thorneycroft-Smith will maintain his current position on the executive boards of the Freight Transport Association, the Variety Club of Great Britain and Brunel University.
He left Iveco, where he had been managing director since December 2005, at the end of June, after 14 years with the van maker.
Eclipse is an independently owned database marketing company based in Reading. The company offers help in database management, direct marketing, systems support, CRM, product recall, contact centre services, case management, market research and web-based marketing.
Eclipse's client roster includes Vauxhall, Kia, Alpro, RBS, and Harley Davidson.