Douglas has been at the agency since 2010 and was one of the first appointments by its global chief executive, Chris Clarke. Clarke took charge of the London office in November 2009 during the merger of Sapient and Nitro.
SapientNitro's senior vice-president and European lead, Dr Christian Oversohl, will also move to Singapore to run the Asia-Pacific headquarters.
As the managing director of SapientNitro Singapore, Douglas will be responsible for expanding the business in Asia-Pacific and handle clients such as HSBC, Unilever and Coca-Cola.
SapientNitro's senior-vice president and managing director, Nigel Vaz, will now take over across the UK and Northern Europe on a full-time basis. Douglas joined SapientNitro from Mindshare. He replaced Kate Howe, who left to become the president of DraftFCB London.
Douglas was previously at a number of advertising agencies including Abbott Mead Vickers BBDO, Leo Burnett and Publicis.
Douglas said: "Coming to London 20 years ago was about learning my craft. Having done that, I am now moving out to a growth market to apply my trade. It will be an exciting adventure and it will be like returning to the 90s, when it was all about growth."