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In an emailed statement, Sorrell said the news "leaves many surprised, including the markets and me."
He went on to discuss the short term implications of Trump's win.
Sorrell said: "Increased levels of uncertainty will mean more hesitation to make important decisions in the short term, both by people and governments. But it may accelerate implementation of helpful reforms in the medium term to reduce uncertainty and stimulate investment as a result."
The advertising chief believes immigration, trade, and terrorism were the key issues that swayed voters in Trump's direction - similar concerns that led the UK public to vote for the country to leave the European Union in June.
Last month, WPP saw a slowdown in growth in its UK revenue, which Sorrell commented could reflect "the first signs of Brexit anxiety" - as marketers tend to be cautious with their ad spend at times of uncertainty.
With those two major political events compounded, Sorrell said: "There will now be a lot of reassessment, including of polling techniques. Electorates at times like these clearly don't like to be told how they're going to vote, especially by the media and other elites."
Sorrell signed off his statement with the news that he and his wife Cristiana Falcone, welcomed the birth of their child on Tuesday. Sorrell, aged 71, also has three grown up sons with his first wife, Sandra Finestone.
Sir Martin Sorrell's full statement on the US election result:
"Effectively a second Brexit that leaves many very surprised, including the markets and me.
It's going to take a significant amount of time to assess the implications beyond the short term.
Increased levels of uncertainty will mean more hesitation to make important decisions in the short term, both by people and governments. But it may accelerate implementation of helpful reforms in the medium term to reduce uncertainty and stimulate investment as a result.
Clearly immigration, trade and terrorism were key issues that swayed electoral opinion in a very significant way, just as they did in the UK, and probably will in the European referendum and elections to come.
There will now be a lot of reassessment, including of polling techniques. Electorates at times like these clearly don't like to be told how they're going to vote, especially by the media and other elites.
One unsurprising event - Baby Sorrell was born on Election Day in New York. A welcome to a rollercoaster world."