Geary, who comes from RG/A's London office, will lead Proximity's producer team in the agency's digital division.
Prior to working at RG/A, Geary spent four years at OgilvyOne as head of production.
Her appointment is one of several at Proximity designed to strengthen the direct marketing agency's digital capabilities.
The other senior digital appointments include Andy Farmer, who joins Proximity's planning team as a digital web strategist.
Farmer previously worked as a director at digital agency Design UK, where he was responsible for helping a range of retail clients develop online strategies.
Sophie Kasriel has also been appointed digital account director and will head up the Allianz and Shell accounts. She joins from Euro RSCG 4D Digital.
Separately, Sepas Seraj from has been appointed technical director and Chris Georgiou has been made web art director. He joins from GT.
Mark Iremonger, Proximity London's head of digital, said: "It's fantastic to have such great talent coming into the agency. The breadth of digital and direct skills in the building make it an incredibly interesting environment to work in."