King took charge of all of Publicis Groupe’s British operations and agencies last month when she started as its first UK chief executive.
The French ad group is pushing a "Power of One" strategy and wants all its agencies to operate under a single P&L for each client in each major country to break down silos and encourage collaboration.
The appointment of Barnes-Austin (pictured, above) as the first UK chief financial officer of Publicis Groupe is significant because it underlines the fact that King has financial responsibility for the UK operation.
Barnes-Austin spent the last two years at Karmarama as chief financial officer, joining the creative agency six months before its sale to Accenture Interactive in 2016, and departed earlier this year.
King (pictured, above) and Barnes-Austin both used to work at WPP’s Ogilvy Group.
She spent 18 years at Ogilvy Group, rising to be UK chief executive, and he worked there for 15 years, lastly as chief operating officer.
King said: "James is the perfect partner to help deliver our vision of Power of One across our UK agencies, which will be pivotal in transforming and growing our client relationships.
"His experience, precision and collaboration will be crucial in driving our UK country model."
Publicis Groupe’s decision to move to one financial operation in the UK contrasts with rivals such as WPP and Omnicom, which have creative, media and other divisions in silos with separate P&Ls.
WPP promoted Karen Blackett to be its first UK country manager in January but the UK operation does not have one P&L or a UK chief financial officer.
Arthur Sadoun, the global chief executive of Publicis Groupe, insisted at an investor day in London in March that its subsidiary agency brands such as Saatchi & Saatchi, Leo Burnett, Bartle Bogle Hegarty, Starcom and Zenith remain important despite the move to one P&L for each major client.