Sir Chay Blyth (born 14 May 1940) is a British yachtsman and rower.

In 1966, whilst in the Army, Blyth together with Captain John Ridgway rowed across the North Atlantic in a 20ft open dory. After successfully completing this in 92 days Blyth was awarded the British Empire Medal. Blyth followed this by moving into sailing and in 1971 became the first person to sail non-stop westwards around the world and as a result was awarded the CBE.

In 1973, Blyth skippered the yacht Great Britain II, with a crew of paratroopers, which took line honours in the Whitbread Round the World Yacht Race, and in 1978 won the Round Britain Race in the yacht Great Britain IV.

Blyth was co-skipper on Virgin Atlantic Challenger I and Virgin Atlantic Challenger II in 1985 and 1986 respectively, before founding the Challenge Business to organise the 1992/1993 British Steel Challenge in 1989. This event allowed ordinary people to sail around the world in a professionally organised race.

The British Steel Challenge was followed by two successive BT Global Challenge races in 1996/7 and 2000/2001. However, a downturn in the sponsorship market meant that the 2004/2005 Global Challenge race set off without a title sponsor.

In 1997, Blyth was knighted by Queen Elizabeth II for his services to sailing.