Even though his objective is to talk about how to stop the proliferation of nuclear material and weapons of mass destruction, the prime minister's schedule was packed with a series of bilateral discussions with European countries, which have been struggling to contain their debt crisis.
Harper and his officials, including Foreign Affairs Minister John Baird, met with Italian Prime Minister Mario Monti almost immediately after stepping off the plane.
Although it's not officially on the summit agenda, North Korea stole the initial headlines after U.S. President Barack Obama challenged the leaders of the rogue regime "to have the courage to pursue peace."
His demand came as Seoul warned it might shoot down a North Korean rocket carrying a satellite if it violates South Korean territory.
Baird acknowledged the distraction, but suggested it should not hijack the conference.
"We're obviously tremendously concerned by North Korea's nuclear program," he said. "We're working with our allies and others to take every diplomatic measure necessary to send a very strong message to the North Korean government that we strongly disapprove."
The launch, which also worries Japan, has been described by the United States as a test of Pyongyang's ballistic missile technology. It's a charge the new regime of Kim Jong Un denies.
North Korea has claimed in the past that its missile tests were benign and only meant to put satellites into orbit. The regime of the late Kim Jong Il launched one of its Taeopodong-2 rockets prior to conducting an underground nuclear test in the spring of 2009.
Those events drove South Korea into joining Proliferation Security Initiative, a global effort to stop the spread of weapons of mass destruction launched in 2003.
Obama, despite his challenge to the North, said he stood by his pledge for a world without nuclear weapons.
A series of internal briefings, prepared for Defence Minister Peter MacKay, show Canada is skeptical of the pledge, especially in light of the regular sabre rattling on the Korean peninsula.
"North Korea's nuclear test provides stark relief to the recent swell of international political support for nuclear disarmament and demonstrates how difficult it will be to translate the vision of a nuclear-free world into reality," said a May 26, 2009 analysis.
Baird said Obama's goal is laudable, but declined to say whether he thought it was practical.
"If we could live in a world that's free of nuclear terrorism, that would be inspirational," he said.
The Harper government was expected to face backroom criticism at the security summit over a recent deal signed by Ottawa-based Nordion Inc., the world's largest supplier of medical isotopes.
It signed a 10-year agreement to buy its supply of highly-enriched uranium from Russia, something that arms control advocates claim has slowed the drive to get bomb-grade material out of circulation and away from potential terrorists.
The U.S., France, Belgium and the Netherlands announced a deal Monday which is meant to sustain the supply of lifesaving isotopes without the use of highly enriched uranium.
Each of the countries declined to criticize Canada directly, but suggested there would be a price to pay for not pushing harder towards low-enriched uranium.
"There's going to be a cost to any country if this material does fall into the wrong hands," said U.S. Energy Secretary Steven Chu. "There's going to be a worldwide cost. We feel it's very important for all countries to recognize that this is a very important step forward."
But Canadian officials were quick to counter by pointing to the country's role in helping other nations like Mexico to convert their reactors from using highly-enriched uranium to low-enriched uranium.
Canadian, U.S. and Mexican officials announced late Monday that the change over of Mexican power plants is complete.
Baird said the Canadian government is committed to eliminating the use of high-enriched uranium, but "in a calm, orderly fashion."
Medical isotopes is big business for Canada because it the world's largest supplier.
Earlier in the day, before arriving at the nuclear security summit, Harper took a first-hand look at the devastation caused by the 2011 earthquake and tsunami in northeastern Japan.
He made a stop in the small Japanese town of Yuriage, outside of Sendai. The city of about one million in the country's Miyagi Prefecture was at the centre of last year's disaster, which killed more than 19,000 people.
Over a year later, signs of the magnitude 9.0 earthquake and massive tsunami were everywhere.
"It's really quite overwhelming to see the scale of the destruction," Harper said.
"I stand here today, one year later, with profound admiration for those who have fought through adversity and pain to rebuild their lives and this region," Harper said in a statement.
"It epitomizes the resolve, resilience and spirit of the Japanese people.”
Harper toured a junior high school, which lost 14 students and 20 parents, all swept away by the massive wall of water.
Desks, debris, bits of papers with half-completed assignments and colouring were scattered over the floor. Water-logged books remained on the shelves and the school clock was stopped at 2:46 p.m., the precise time the tsunami hit.
Sumio Takahashi, the school's principal, showed Harper around and said it's tough to enter the building.
In some areas the wave reached eight kilometres inland.
The only signs of where entire subdivisions once stood were the outlines of foundations in the sea-spoiled soil.