Langdon, ousted earlier this year as McCann-Erickson Worldgroup's regional director, and Wnek, the chairman of the Euro RSCG group, are launching with a unnamed planner and a finance chief.
Langdon, Wnek and the planner will have their names on the door and although plans are at an early stage, the intention is to set up from January.
Langdon told Campaign: "Our core philosophy is big, experienced people and big advertising ideas - without all the pain of going to a big agency."
News of the venture follows months of rumours about the intentions of the pair, who came close to working together for the first time when Wnek was mooted as the executive creative director at McCann earlier this year.
Wnek was appointed as the co-chairman of the merged Euro RSCG Wnek Gosper and Partners BDDH agencies in August.
Wnek said: "I'm glad to leave the London agency on a high and with a great new team at the helm."
Jim Heekin, the president of the Euro RSCG network, said of Wnek's departure: "This is a mutual thing." He added that he would appoint a chairman of the UK group soon.