Latham has served on the Board of Opex since it acquired INM in 2002.
He left the company when his three-year post acquisition agreement expired in July but continues to work on some outstanding projects on a consultancy basis.
Latham founded INM in 1990 with Fergus Mitchell, who will remain as the sole managing director following Latham's departure.
Latham and Mitchell together pioneered event television for organisers worldwide, distributing content from events such as ITU World Telecom via satellite, cable, terrestrial, digital TV and the web.
Opex chairman Guy Morgan said: "It has been an enormously rewarding partnership. Latham is a maverick who has pushed the boundaries of marketing and operational protocol."
Meanwhile, Opex has purchased more than £1m worth of shell schemes from supplier Octanorm UK as it moves into a two-year rolling stock refurbishment and replacement programme.
"Organisers have been negotiating hard on price, which has had an effect across the board on quality," said Opex Group managing director Andy Gibb.
"We will maintain quality levels so organisers will be confident in Opex's stock. We presented eight shell scheme options to the Association of Exhibition Organisers in December 2004, two of which were then presented at International Confex. But we received no orders so concluded that people still want Octanorm. We are therefore not investing in new systems but are committed to ensuring the quality of our existing products."