Harper flies first to Warsaw, where he will join U.S. President Barack Obama and other world leaders Wednesday to mark what the Prime Minister's Office said is the 25th anniversary of Poland's emergence from communism.
On June 4, 1989, Poland's anti-communist Solidarity movement officially won power in democratic elections.
Harper then travels to Brussels to attend a G7 summit, which was arranged hastily to replace a G8 meeting scheduled for Sochi, Russia, scrubbed in the wake of the crisis in Ukraine.
He ends his trip in Normandy, where he'll attend D-Day ceremonies, an event which is expected to include Russian President Vladimir Putin.
Harper hasn't expressed any desire to speak to the Russian leader, although it's likely he will speak to others about Putin.
The prime minister labelled Putin a threat to world peace after Russia annexed the Crimean Peninsula. Harper blames the Russian leader for instigating continuing unrest in eastern Ukraine.
Last week, Harper denounced Putin in a strongly worded speech in Toronto. He tied Putin to the worst evils of 20th century communism, which he called a ruthless and "poisonous ideology."
Shortly after Harper's departure Tuesday, New Democrat MP Paul Dewar urged him to shelve the rhetoric and start promoting concrete steps to help Ukraine.
"The prime minister needs to engage with our international partners at the G7 meeting with regards to Ukraine to encourage dialogue and pursue a diplomatic resolution to the crisis," Dewar said.
"We need to support strategic economic investment, particularly in areas like energy efficiency."
In addition to Russia and Ukraine Harper has also said that once he's in Brussels, he'll lobby his fellow leaders to come up with more money for his signature initiative on maternal and child health. He's also expected to talk jobs and the global economy.
Harper's Warsaw visit will contrast a vibrant Poland that has become an Eastern European success story with an economically hobbled Ukraine struggling to escape the influence of Putin's Russia.
Harper will meet Polish Prime Minister Donald Tusk to discuss the world's response to the crisis in Ukraine.