Sullens is set to leave UBM on 27 September to move to Future media group, to set up an events portfolio and told C&IT he "wasn't looking to leave UBM but this opportunity came up through different conversations".
Future has offices in London - where Sullens will be based - and Bath, and has a focus on technology, gaming and music, producing magazines including T3.
As Future's new head of events, Sullens' brief is to develop conferences and events as a significant revenue stream for the business.
Future chief executive Mark Wood said: "We see this area as a significant new revenue opportunity for the company. Jonny has the perfect combination of energy and experience to head up this exciting new business at Future – I’m delighted to have him coming aboard."
UBM Live will be announcing Sullens’ replacement in the next few weeks, but said that in the meantime it is business as usual for International Confex.
UBM managing director Simon Parker said: "We can’t thank Jonny enough for the massive contribution he has made to his show products. Over the past five years he has had a dramatic influence in securing the long-term future of the shows and given us a strong platform for further growth.
"Leisure Industry Week remains a flagship show for UBM Live and one that continues to enjoy phenomenal success in its industry. Meanwhile, International Confex continues to be both the market leading exhibition in the meetings and events industry and one of its most powerful brands."
Confex moved to Excel in March this year after 16 years at Earls Court and Sullens said: "I am really pleased with what we have achieved with Confex and we have some great initiatives for 2013."
He added that he will be making a "clean break" once he moves to Future: "The team I have that run all the individual shows [at UBM] know their products and markets inside out."
International Confex and Live Experience event manager James Samuel said: "This is a really exciting period for both shows as more and more exhibitors sign up this year. The launch of Confex Week earlier in the summer has also given us the perfect platform to build on our existing partnerships both within and outside the industry and to expand new ones."
International Confex and Live Experience take place 19-21 March 2013 at ExceL London.