Damon Collins and Richard Exon, the former chief executive and executive creative director at Rainey Kelly Campbell Roalfe/Y&R, brought in Upton and Lori Meakin as co-founders and minority shareholders when the agency launched in May 2012.
Prior to co-founding Joint, Upton worked at Mother from 2004. He worked at Bartle Bogle Hegarty from 1998 to 2004.
Collins and Exon said: "It’s been great working with Nik, we thank him for everything he's done for Joint and we wish him every success in the future."
Upton said: "I am very proud of Joint and what we have achieved. But I wish to pursue new ventures and would like to thank my partners for all their support in letting me do this."
Meakin, a former joint head of planning at RKCR/Y&R, continues to lead strategy at Joint.