Pemsel, who previously reported to ITV's outgoing managing director of brand and commercial Rupert Howell, was told last week that ITV's director of television Peter Fincham will take over the broadcaster's marketing and research budget.
Chad Wollen, ITV's director research and insight, is also leaving the firm as part of major changes to the senior management team.
ITV plans to run a recruitment campaign for both positions, with the group marketing director role likely to be filled by an external appointment.
Speaking to The Guardian, Fincham said: "ITV is an iconic brand and the challenge is to ensure that it is both powerful and relevant in an increasingly crowded multimedia and broadcasting landscape.
"The changes also give us the opportunity to harness the strengths of our marketing and research teams, who will work together to help us develop strong programme brands."
After joining ITV in October 2005, Pemsel was promoted to group marketing director in January 2007.