Antoniades, who has been appointed managing director, global business, will also be responsible for managing key global client relationships run outside the US, including UBS, Bel and King.
For the past five years, he has led the operations for Starcom Mediavest Group across the Middle East and North Africa as regional chief executive. Antoniades is credited by leading successful new-business pitches in the region for clients including Visa Fiat Chrysler and Merck.
Before 2012 he worked for six years in EMEA client director roles for Starcom Mediavest, having started his career at Mediavest in London as a planner in 1995.
In his new role, Antoniades will also work closely with Spark Foundry’s global executive team to ensure its new brand positioning is implemented across all international markets.
He reports to Chris Boothe, US chief executive for Spark Foundry.
Publicis Media announced Mediavest Spark’s rebrand to Spark Foundry last week, ending speculation that the agency would be merged with Starcom or Zenith.
Boothe said: "In John we have an incredibly talented, dynamic and accomplished leader and his impressive track record demonstrates his ability to grow markets, innovate and provide excellent leadership."