He has been briefed to oversee creative and lead innovation across 24 markets and will also retain responsibility for the UK.
Bailey has been at Isobar since March 2013. He was previously at AKQA, joining as a senior copywriter in 2004 and moving up to associate creative director, creative director and then executive creative director at AKQA Amsterdam in 2009.
Steven Moy, the chief commerce officer at Isobar US, will become the chief executive of Isobar UK.
He will also be in charge of eCommera, the e-commerce agency that Isobar UK acquired in June. Moy will bring the agencies "closer together, further strengthening their brand commerce offering".
The pair will report to Tracy De Groose, the UK and Ireland chief executive of Dentsu Aegis Network, and start their new roles in January.
Before joining Isobar in 2013 Moy worked at SapientNitro on growing the business and "defining its service offering in omni-channel marketing and commerce".
Jon Boardman, the managing director at Isobar, has left the company. He joined the agency in May last year and was previously at VCCP.
Jean Lin, the global chief executive of Isobar, said: "Clients want to integrate brand experience with commercial interactions so we have designed our organisation and leadership to respond to this.
"Steven’s appointment enables us to be best-in-class in brand commerce. Nick’s promotion means that their joint experience will form a powerful offering for our clients."