President Vladimir Putin, the longest-serving Kremlin chief since Josef Stalin, stood beside Xi, several dozen other leaders and Russian veterans on a roofed tribune beside Vladimir Lenin's mausoleum on Red Square as Russian troops marched past.
Putin said Russia would never accept attempts to belittle the Soviet Union's decisive role in defeating Nazi Germany, but that Moscow also recognised the part played by the Western allies in defeating Adolf Hitler.
"The Soviet Union took upon itself the most ferocious, merciless blows of the enemy," Putin said on Friday.
"We shall always remember that the opening of the Second Front in Europe after the decisive battles on the territory of the Soviet Union brought victory closer."
"We highly appreciate the contribution of the soldiers of the Allied armies, the members of the resistance, the courageous people of China, and all those who fought for a peaceful future to our common struggle."
The war in Ukraine, Europe's deadliest since World War Two, haunts the celebration.
Some 1500 of the 11,000 troops in Red Square have fought in Ukraine, and drones - the biggest technological innovation of the war - were due to be paraded for the first time.
Ukraine attacked Moscow with drones for several days this week, though there were no reports of major attacks on Russia on Friday amid a 72-hour ceasefire declared by Putin.
Moscow and Kyiv do not publish accurate casualty numbers for the war in Ukraine, though US President Donald Trump, who says he wants peace, says hundreds of thousands of soldiers on both sides have been killed and injured.
The Soviet Union lost 27 million people in World War II, including many millions in Ukraine, but pushed Nazi forces back to Berlin, where Hitler committed suicide and the red Soviet Victory Banner was raised over the Reichstag in 1945.
Chinese Communist Party historians say China's casualties in the 1937-1945 Second Sino-Japanese War were 35 million.
Nazi Germany's unconditional surrender came into force at 11.01pm on May 8, 1945, marked as "Victory in Europe Day" by Britain, the United States and France, while in Moscow it was already May 9, which became the Soviet Union's "Victory Day" in what Russians call the Great Patriotic War of 1941-45.
For Russians - and for many of the peoples of the former Soviet Union - May 9 is the most sacred date in the calendar, and Putin has sought to use memories of World War II to unite Russian society, especially amid the war in Ukraine.
The Kremlin says the attendance of Russian allies such as Xi, Brazilian President Luiz Inacio Lula da Silva and several dozen leaders from the former Soviet Union, Africa, Asia and Latin America shows Russia is not isolated even if Moscow's former WW2 Western allies want to stay away.
Chinese troops took part in the parade, and some North Korean soldiers in uniform were spotted watching the parade in Moscow.
Putin has sought to insulate Moscow from the grinding artillery and drone war being fought 600km away in Ukraine, though Ukrainian drone attacks have in recent days disrupted air travel to the Russian capital.
Some drone attack warnings were announced overnight in some western Russian regions but there were no reports of attacks on Moscow.
Putin proposed a 72-hour ceasefire until May 10, though Ukraine said Russia had broken the ceasefire, a claim dismissed as absurd by Moscow.
