Spencer replaces director of regional sales, David Croft, who was one of six executives to leave the broadcaster earlier this year after a restructure of the sales department by new managing director of commercial and online, Fru Hazlitt, and chief executive Adam Crozier.
With responsibility for ITV's dealings with regional agencies and clients, Spencer will report to ITV's director of TV sales, Kelly Williams.
Prior to heading up PHD North, Spencer held roles at PHD London, Carat and the Manchester Evening News.
Hazlitt said: "We have pledged to work differently with our clients and customers and Jason's appointment is a key part of extending this new way of working across our regional customers.
"ITV's regional operation gives us a unique position in the market and Jason possesses the strategic acumen, commercial talent and enthusiasm to improve and build on this."
Spencer said: "After eight wonderful years at PHD, the opportunity to join ITV as regional sales director was too good to turn down. With plenty of exciting challenges ahead and as the transformation plan gathers momentum, this is a great time to join."