The event kicks off two days of D-Day anniversary commemorations, which will continue in Normandy on Thursday.
US President Donald Trump, Queen Elizabeth II and 300 veterans, many of whom are in their 90s, will hold a ceremony on the south coast of England. French President Emmanuel Macron and other world leaders will then join them in Portsmouth, the main departure point for 156,000 US, British, Canadian and other Allied troops sailing to the beaches of northern France.
Britain has promised "unprecedented commemorations" in Portsmouth, with testimony from some of the veterans and "one of the greatest British military spectacles in recent years" featuring a flyby of 24 vintage and modern military aircraft.
Commemorations in France on Thursday will be held at military cemeteries near the Normandy beaches where Allied troops landed and died.
Declaration of shared values
In a joint D-Day proclamation marking the anniversary, the 16 nations attending Wednesday's ceremony affirmed their shared responsibility to ensure that the horrors of World War II are never repeated.
"Over the last 75 years, our nations have stood up for peace in Europe and globally, for democracy, tolerance and the rule of law," it said. "We re-commit today to those shared values because they support the stability and prosperity of our nations and our people. We will work together as allies and friends to defend these freedoms whenever they are threatened."