The Omnicom agency won the account after a competitive pitch that involved four agencies. AAR assisted with agency selection.
The business moves from Starcom, which had worked with Betway for seven years until the end of last year. OMD will start working on the account from next month.
Betway plans to launch a global campaign in 2019 to support its growth into new markets.
The brand, which offers online poker, casino and bingo as well as sports betting, is the shirt sponsor of Premier League football club West Ham United.
It has also recently kicked off a review of its UK creative account after splitting with Above & Beyond.
Anthony Werkman, chief executive of Betway, said of OMD: "Over the course of the detailed selection process, they demonstrated not only their technical competency, but also their shared commitment to demonstrating our ‘For the love of the game’ philosophy.
"The possibilities this partnership presents us in the UK are incredibly exciting. We look forward to OMD keeping the Betway brand front of mind among our target audience, while adhering to the strict responsible marketing principles that run throughout our business."