O'Connor was previously chief financial officer at Prime Visibility Media Group (PVMG), which was acquired by RhythmOne in 2011 when the latter was called Blinkx.
S. Brian Mukherjee, chief executive of RhythmOne, said: "We are delighted to have Rich join RhythmOne and expect a seamless transition, given his deep Media, Ad-Tech and content distribution experience, and successful history of working closely with several members of the executive team.
"We look forward to his energy and enthusiasm, as we embark on a new chapter in the company's growth."
During his time at PVMG, O'Connor was instrumental in building the finance team, managing the business to strict profitability standards, restructuring operations and the balance sheet, and driving revenue growth, the firm said.
He began his career at Warner Bros. Domestic Television, moved on to MCA TV and, through a series of acquisitions and integrations, held finance roles within Universal TV, USAI and Vivendi Universal - eventually serving as vice president of finance and operations at Universal Domestic Television, a US$1bn division of NBC Universal (NYSE: GE).
Reginelli is stepping down after five years in the role and will be available on an as required basis for up to six months to help with an orderly transition.
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