The Argentinian takes over the job from Adrian Holmes, Lowe's London-based global chief creative officer, who was last year named the chairman of Lowe Worldwide.
Vega Olmos will add Unilever to his existing responsibilities as the chairman of Vega Olmos Ponce, the Lowe agency in Buenos Aires.
His brief is to oversee the work Lowe produces for Unilever across major markets and ensure its continuous improvement. He has already worked with Holmes on Unilever's creative output in Argentina.
During that time he has been honoured at Cannes, the Clio awards and the New York Festivals.
Lowe has had mixed fortunes on its Unilever business over the past year, losing the pan-European Surf business and Flora to Bartle Bogle Hegarty.
However, the network has picked up extra assignments in the US, Canada, Australia and New Zealand.
Before joining Lowe, Vega Olmos worked for the BBDO and Grey networks in Argentina, first as the creative director at Ratto BBDO and later as a partner at Caesares Grey.
In 1997, he linked with Hernan Ponce to form the agency, which two years later became VOP/Lowe & Partners.
Jerry Judge, the Lowe chief executive, described Vega Olmos as "a hugely talented creative leader".
He added: "Since he's already been doing great work for Unilever, we'd expect the calibre of our creative product to continue to get better elsewhere under his leadership."