O'Bric, 33, joins the agency from Rainey Kelly Campbell Roalfe/Y&R, where he worked on accounts including Starbucks, COI (Royal Marines and Royal Navy) and Powergen.
His work on the Virgin Trains account won a silver IPA Effectiveness Award in the Best New Client category in November last year.
Before joining RKCR/Y&R, O'Bric worked at HHCL/Red Cell and Leo Burnett.
He began his career in the strategy and marketing department at MTV in London, before moving to Milan to launch the music TV channel in Italy.
O'Bric said: "Mother is the most exciting and innovative agency in Britain today. It has got a vision and a sense of purpose and a quality of work that is second to none."
The Mother partner Stef Calcraft said: "Garbhan combines a great intuitive mind with a wonderful Celtic sensibility. He joins an extraordinary array of strategic talent at Mother."