Groves will head up the account teams working across the agency's clients, which include Budget Car Rental, Holiday Cottage Group, Axa, Bupa, PDSA and recent additions, Exclaimer and Red.
He joins from full service agency Digivate, where he was head of online marketing overseeing SEO, pay per click, affiliate marketing and email marketing for retail, fashion and financial services clients.
Prior to Digivate, Groves was marketing director at London Scottish Broking, where he oversaw online marketing for two years including websites, search marketing, SEO, affiliate, email and mobile marketing programmes, as well as offline, for brands including Easy Loans and Pacific Home Loans.
Before that he was a director at full service agency Blue Edged Media for three years with responsibility for developing the agency's digital services.
O'Brien said: "After what was a great year with some solid client wins, bringing Mike on board now is key to managing that growth to ensure that we're able to continue delivering the very best service for our clients.
"Mike's first-class digital marketing pedigree and great mix of senior level agency and client-side experience makes him a very valuable addition to the team."