Pictures on state television showed thousands of soldiers marching in formation alongside tanks, balloons and enormous crowds.
Leader Kim Jong Un was shown clapping and smiling from a reviewing box.
At one point, the soldiers directed a chant toward him.
"We will die for you!" they yelled, CNN's Will Ripley, who was at the event, reported.
During the pomp and circumstance at Kim II Sung square, citizens showed their revolutionary fervor with choreographed performances while vehicles displaying North Korea's military arsenal rolled by.
"We saw a submarine launch ballistic missiles, we saw missiles that are capable of being launched from a mobile launcher and just seconds before we came on the air we saw these very large what are believed to be intercontinental ballistic missiles," Ripley said as jets tracked colors of the North Korean flag in the sky during the parade.
In a live broadcast, a newsreader from North Korea's state-run television service called the new military hardware the country's "modernized strategic missiles."
"No nation in the world develops missiles and shows the real thing during a parade, it's just too dangerous," Markus Schiller, a weapons expert with ST Analytics, told CNN that parades always involve "mock-ups". "If anything happens, it blows up, right next to the 'Dear Leader'."
For North Koreans, April 15 is an auspicious date that sees millions celebrate the birth of the nation's founder.
Tens of thousands descended on the streets of the capital as the nation marks the 1912 birth of Kim Il Sung, grandfather of Kim Jong Un.
This year's celebrations come at a tense time on the Korean Peninsula, days after a US strike group was deployed to the region
and amid expectations of another missile or nuclear test by Pyongyang.
North Korean state media
warned that such "reckless acts of aggression" would be countered with "whatever methods the US wants to take."
"If the US does any reckless provocation, we will immediately apply a destructive strike with our revolutionary power. We're prepared to respond to an all-out war with an all-out war and we are ready to hit back with nuclear attacks of our own style against any nuclear attacks," Choe Ryong Hae, a senior member of the Presidium of the Political Bureau of the Workers' Party of Korea (WPK) said in a speech during the large military parade.
Tension has been building since Kim Jong Un announced in his New Year's message
that the country was close to testing an intercontinental ballistic missile.
It has since conducted a number of shorter-range missile tests -- some of which landed in the sea,
less than 200 miles off the Japanese coast.
It's also conducted engine tests that analysts say could potentially power a long-range missile
US President Donald Trump held talks with Chinese President Xi Jinping at his Mar-a-Lago resort last Friday to push his case for China to do more to rein in North Korea's nuclear ambitions. They then spoke Tuesday
by phone, in a call Trump described as "very good."
However, days later, he tweeted: "North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them! U.S.A."
North Korea says it's created a nuclear weapon small enough to mount on a missile, though many experts dispute that claim.
Day of the Sun
The Day of the Sun is a public holiday usually marked by grand military parades,
mass celebrations and other large displays of national pride.
It also often involves shows of force, such as weapons tests or other displays of strength.
In recent days, North Koreans have been seen practicing choreographed dance routines in brightly colored national dress.
Before the event, foreign journalists invited into the country to report on the occasion were entertained by children at the Children's Cultural Palace on the outskirts of Pyongyang.
An enormous amount of work goes into preparing for April 15.
Joseph Bermudez, an analyst for North Korean monitoring group 38 North, said preparations could even be seen on satellite images, which showed thousands of people and hundreds of vehicles practicing ahead of the event.
Monday, hundreds of members of the Korean People's Army (KPA) crowded the plaza of the Kumsusan Palace of the Sun in Pyongyang to pay tribute to past leaders and vow loyalty to Kim Jong Un, according to state media Rodong Sinmun.
Kim Il Sung died in 1994 at the age of 82, after leading his country from its establishment in 1948 until his death.
He passed the leadership to his son, Kim Jong Il,
who in turn passed it to Kim Jong Un.