Interpublic has promoted Philippe Krakowsky to chief operating officer of the group and Daryl Lee to global chief executive of media buying division IPG Mediabrands.
The promotion of Krakowsky, who is already the de facto number two at Interpublic, cements his position as the internal frontrunner to succeed Michael Roth in the top job.
Roth, 73, has been chairman and chief executive of Interpublic since 2005.
The company said Krakowsky will work with Roth "to oversee business operations across Interpublic". IPG has not had a global chief operating officer in more than 15 years.
Krakowsky has worked at Interpublic since 2002 and has most recently been executive vice-president, with dual roles as chief strategy and talent officer of Interpublic as well as chairman and chief executive of IPG Mediabrands.
He will keep his role as chairman of IPG Mediabrands and in his new role will have direct oversight of Acxiom, Carmichael Lynch, Deutsch, Hill Holliday, Huge and R/GA.
Harvard-educated Krakowsky, who is 57, previously had spells at Y&R and BBDO.
He started his career as an entrepreneur, helping to build and ultimately sell an artificial intelligence software development company to Apple.
Roth said: "For more than a decade, Philippe has played a key part in major strategic actions at Interpublic that have been integral to our long-term success, and more recently he was the driving force behind our acquisition of Acxiom.
"He has helped me in the design and execution of our cross agency ‘open architecture’ model that delivers the best of IPG solutions to our clients. He has also been instrumental in helping create IPG’s distinctive culture, which attracts the industry’s best talent. We're very excited to have him positioned in this new chief operating role at IPG."
Lee, 48, has worked at Interpublic since 2006 and has been global chief executive of UM since 2012, after previously holding roles at McCann Worldgroup, McCann Erickson and as head of global strategy at UM.
Recent media account wins have included American Express, Mattel and Just Eat.
As head of IPG Mediabrands, Lee will take charge of agencies including UM, Initiative, performance agency Reprise and out-of-home shop Rapport.
Lee was born in Zimbabwe, grew up in South Africa and studied at University of Oxford, before starting his career as an associate at McKinsey & Company and then moving to Ogilvy & Mather.
Roth said: "Daryl is one of our industry’s top business strategists, with experience as a management consultant, at creative agencies, as well as in the media sector.
"He is relentlessly client-focused, and has consistently proven that he and his teams can identify insights-driven, creative solutions for marketers’ most challenging problems.
"Daryl’s great passion for the business inspires his people to do their best work, and he has consistently shown himself to be a true champion for diversity and inclusion, a core IPG value."
Interpublic has been the strongest performer of the big six global agency holding companies in recent years, posting 5.5% organic growth last year and 4.6% in the first six months of 2019.
IPG Mediabrands, the world’s fifth-largest media buyer, has also grown strongly, increasing billings by 7.2% to $16.5bn globally last year, according to an estimate by COMvergence. UM’s billings grew 3.7% last year.
Eileen Kiernan, most recently global president of J3, a dedicated unit for Johnson & Johnson, is promoted to replace Lee as global chief executive of UM.
Interpublic has been preparing for generational change.
Frank Mergenthaler, the long-serving executive vice-president and chief financial officer at Interpublic since 2005, announced in June that he would step down at the end of this year and hand over to Ellen Johnson, global chief financial officer at IPG Mediabrands.
Interpublic employs almost 55,000 people. Other agencies include PR shops Weber Shandwick and Golin.