The monarch, dressed in a pink ensemble, arrived at the coastal city for the ceremony, where droves of allied forces left the UK to invade France and fight liberate Western Europe from the Nazis in 1944.
The Royal Family had earlier posted a tribute to WWII troops on its Instagram account.
"Tomorrow is #DDay75 – the anniversary of what is considered one of the largest military operations in history. Over 5,000 vessels and ships, nearly 11,000 planes and over 130,000 ground troops landed in Normandy, France during WW2.
"Later today, The Queen, The Prince of Wales, President Donald Trump, Mrs Trump and other world leaders will attend a National Commemorative Event in Portsmouth to mark #DDay75.
"📷 1 and 2 are photographs taken from D-Day and show troops landing on the Normandy beaches, some having set off from Portsmouth.
"📷 3 and 4 show the landing beaches and tide clock used in the planning for D-Day at Southwick House, Portsmouth."