Macron's visit with Harris to NASA offered the two countries a chance to show off their cooperation on space technology.
During her meeting with the French leader, Harris said France was a "vital ally" of the United States while both underlined the importance of their space cooperation.
In June, France signed the Artemis Accords which aims to support NASA's goal of returning humans to the moon by 2024. In the same month, the US joined a French initiative to develop tools for adapting to climate change called the Space for Climate Observatory.
Iran nuclear program and China on agenda for Biden meeting
Macron and his wife are also due to meet President Joe Biden and the US president's wife for a private dinner later in the day. On Thursday, Macron will attend an official welcoming ceremony hosted by Biden at the White House.
Following the talks, Macron and his wife will attend a state dinner with musician Jon Batiste set to perform.
NASA heads back to the moon with Artemis 1
France pushing for peace talks in Ukraine
Both the US and France are closely supporting Kyiv forces fighting Russia in Ukraine. But differences remain — Macron has repeatedly called on Ukraine to resume peace talks with Russia. However, Biden has maintained that this decision is solely in the hands of the Ukrainian leadership.
An advisor to Macron told the AFP news agency that France and the US are "not allies on the same page" and promised "challenging" talks with Biden.
Separately, French government spokesperson Oliver Veran on Tuesday said that there is a need for "re-synchronizing" of the agendas.
White House National Security Council spokesman John Kirby said that Washington is "in the mode of listening and making sure we understand concerns by our European partners," while also praising Macron for his "experience and wisdom."
Tensions have also been simmering between the US and its European allies after Biden enacted the Inflation Reduction Act — which authorizes subsidies for climate and energy initiatives. The French president called the legislation "unfriendly" and that it could upend the "level playing field" in international trade.