The move sees Watt team up with former colleague Melissa Rowling, who Watt worked with at Weber when the agency was called Weber Shandwick Square Mile.
He joins as strategic communications director.
Watt will work with Greentarget MD Nick Glanvill and Rowling, who is the agency's MD of PR.
Prior to Weber Shandwick Financial, Watt was a director at Bell Pottinger Corporate and Financial.
'Jeff has spent over ten years advising major financial brands, both in the UK and internationally. Clients will value the depth of sector expertise that he brings and his ability to implement complex integrated communications programmes,' said Glanvill.
Greentarget is now 20 strong, having formed 19 months ago (PRWeek, 21 September, 2006).