The New Zealand prime minister is in the US on a multi-faceted trip built around Harvard University's Commencement address, which she has been invited to deliver on Friday.
Kiwi officials are yet to be advised whether Ms Ardern will be given an audience with President Joe Biden.
In the meantime, she met with the head of the United Nations, asset managers BlackRock and gave interviews to some of the world's leading travel publications, all on a bumper day one.
The trip has been designed to promote New Zealand to the world and help ailing tourism operators back onto their feet after two years without international visitors.
The appearance on The Late Show was to focus on Ms Ardern's pitch, but the tragic school shooting in Uvalde, Texas naturally took top billing.
Mr Colbert began his show with an impassioned plea for gun control, saying "I'll tell you who've done something about it - the New Zealanders".
After introducing Ms Ardern, Mr Colbert invited her to explain New Zealand's gun law reforms that followed the 2019 Christchurch Mosques attack.
"When I watch from afar and see events such as those today I think of them not as a politician, I see them just as a mother and I am so sorry for what happened here," she said.
"We are a very pragmatic people. When we saw something like that happen, everyone said 'Never again'.
"We have legitimate needs for guns in our country for things like pest control ... but you don't need a military-style semi-automatic weapon to do that. So we got rid of them."
Mr Colbert pivoted to the purpose of the interview - spruiking Kiwi tourism, allowing Ms Ardern to give her best sell-job.
"We are open," she said.
"Welcoming guests to New Zealand is so much of who we are. Hospitality is part of our identity ... please, come back and make us whole again, you'd be so welcome."
Ms Ardern is no stranger to the sho. She has appeared multiple times and forged a friendship with Mr Colbert due to his love of New Zealand and the Lord Of The Rings, where the movie adaptation was filmed.
Wearing what local NZ outlet Newsroom described as a "banging bright pink pant suit" by Kiwi designer Juliette Hogan, Ms Ardern went on to describe her family life with partner Clarke Gayford and daughter Neve, and their recent coronavirus diagnosis.
"I got COVID for Mother's Day. That was Clarke's gift to me," she said.
That bout of COVID-19 has been cited by Ms Ardern's office as the reason she is yet to land a meeting with Mr Biden, with the White House operating under strict pandemic protocols.
Ms Ardern said a morning meeting with UN Secretary General Antonio Guterres was centred on climate, sustainability and the war in Ukraine.
She is travelling with trade minister Damien O'Connor and a business delegation, and was pleased to be able to host a meeting with BlackRock on their behalf.
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