The prime minister joined Russian President Vladimir Putin at a leaders' luncheon after starting the day by laying a ceremonial wreath at the Beny-sur-mer Canadian Cemetery, where more than 2,000 men killed on D-Day, most of them Canadian, are buried.
Harper arrived at the luncheon hosted by French President Francois Hollande before the start of the major International Ceremony of Remembrance commemorating the June 6, 1944, offensive.
Putin's long anticipated arrival came as U.S. President Barack Obama, German Chancellor Angela Merkel and British Prime Minister David Cameron and other world leaders assembled for the day's events.
Prior to the lunch, Harper stood smiling straight ahead from the second row of a large family photo of world leaders, as Putin slipped into the front row that included the Queen, Obama and Hollande, among others.
France invited Putin to the D-Day anniversary, a decision Harper supports because he says it reflects the vital contribution the former Soviet Union made in helping Allied forces defeat Nazi Germany.
Harper has said he will steer clear of Putin altogether, and Obama says he won't be going out of his way to meet the Russian leader either but will talk to him if they meet.
Obama and Harper tried to persuade Hollande, Merkel and Cameron to not meet with Putin while the leaders were discussing the week's events at the G7 summit earlier this week.
In the end, they all agreed that the three European leaders would use their meetings with Putin to express the G7's strong condemnation of the Russian leader's annexation of Crimea and fostering of unrest in eastern Ukraine.
Harper will end the day at Juno Beach where 18,000 Canadian troops launched their contribution to the massive Allied attack on Europe that changed the course of the Second World War.
Canada's D-Day tribute to the 359 Canadians who died on the first day of the battle was unveiled Thursday at the Juno Beach Centre — comprised of 359 maple tribute markers.
Juno Beach is now a serene eight-kilometre strip of summer resorts and villages scattered over flat land behind low beaches and a seawall.
In written statement earlier in the day, Harper lauded the courage of the young Canadians on that historic day.
"It is difficult to understand the courage it took to advance through minefields and barbed wire under fire from mortars and machine guns in order to punch through Hitler's Atlantic Wall; and yet that is exactly what many Canadians did," Harper said.
He said Canadian can take enormous pride in the fact their troops played "such a pivotal role in ensuring the success of the D-Day landings," which he called a turning point in the world's history.
"We are also deeply humbled by the enormous sacrifices made by our fellow citizens, who with grim determination, stood shoulder to shoulder with like-minded allies to fight evil."
Some 130,000 U.S., British and Canadian troops stormed the 80-kilometre stretch of beaches along the French Channel coast to attack hundreds of Nazi troops in concrete fortified gun positions.
Canada suffered more than 18,000 casualties, with 5,000 killed in the 2 1/2-month campaign, which eventually led to Europe being wrested free of German occupation.
For half of the members of D Company of Queen's Own Rifles, it would be the place they would lose their lives in the first moments of setting foot on European soil as they sprinted 180 metres from the water to the seawall.
At Juno Beach Centre, Harper and his wife Laureen are to be greeted by French Prime Minister Manuel Valls, and a large group of Canadian veterans who fought at Normandy.
The Canadian 3rd Infantry Division fought alongside the British 3rd and 50th Infantry Divisions and the U.S. 1st and 4th Infantry Divisions.