Simpson, who was 39, had long suffered from asthma. Friends and associates said that he would work from home rather than go to the office if the air pollution in Hong Kong was too high.
Simpson's experience spanned more than 15 years and two continents, after he started his advertising career in a small agency in Oxford, UK in 1984.
He was part of the British advertising scene until 1991 when he made the move to Asia to take up the post of associate creative director at Leo Burnett Hong Kong. He later went on to take up the role of Hong Kong CD at Euro RSCG and then at M&C Saatchi.
Simpson was head copywriter at Lowe Hong Kong, a post he was in for just six weeks before his death.
Simpson was a multi-award winner at some of the top shows in the world, including Cannes, D&AD, London Festival, New York Festival, Clio, Media's Advertising Awards, the Hong Kong 4As Creative Awards and the Singapore Creative Circle.
Former colleagues at M&C Saatchi were the first to heap praise on Simpson.
Head of creative, Tan Khiang, said: "Keiron is a craftsman, toiling to get the perfect headline, and unafraid to let you know he has not got it. It is passion that drives him. Keiron will think and mindmap to arrive at solutions that are refreshing."
Ian Thubron, the former head of M&C Hong Kong, said Simpson's death represented the loss of a "great talent".
"Undoubtedly, he was one of the strongest English copywriters in Hong Kong. He was responsible for a number of very high-profile ads, including Mandarin Oriental Hotel, HK Standard and Gallery 13," said Thubron who is now the group managing director of Ogilvy & Mather Shanghai and national director for international clients.
Stanley Wong, founder of production house, Three-twoone, said that Simpson had "an unconformed kind of attitude" towards creativity. He added that when they last met a couple of months ago, Simpson talked and painted at the same time.
"It's that passion, which Hong Kong has lost,"Wong said.
Simpson leaves behind three children - Harvey, Daisy and Sam aged between five and 13 - and a wife, Michele.