The expansion aims to bridge the gap between European luxury brands and affluent Asian customers.
The integration brings together more than 8,000 media and performance specialists across 93 key global markets.
Ng, who is Malaysian, has helmed leadership roles at Isobar, Digitas, and BBDO throughout his career.
The transformation programme includes all service lines, functions and central teams, and will initially be led by its largest markets which cover more than 80% of dentsu international's revenue.
Reprise Commerce is responsible for designing and executing customer-centric strategies across all stages of the eCommerce journey, including eRetail, supply chain and warehousing, marketplaces and D2C.
Roth will assume the role of executive chairman of the board next January. He took on the CEO role in 2005.