Koch and Meir were expected to spend more than five hours outside the space station to replace a failed power controller, but extended their spacewalk to "accomplish some get-ahead tasks on the space station," according to NASA.
The astronauts spoke with President Donald Trump and Vice President Mike Pence during the spacewalk.
The conversation marked the first time since the 1969 moon landing that a sitting president spoke directly to astronauts who were physically outside of a spacecraft in space, according to the White House.
Trump called the two astronauts "very brave people" for their service on the space station.
"I don't think I want to do it. I must tell you that. But you are amazing people," the president said, later adding, "You're very brave, brilliant women."
"At the same time, we recognize that it is a historic achievement and we do of course want to give credit for all those who came before us," Meir added. "There has been a long line of female scientists, explorers, engineers and astronauts and we have followed in their footsteps to get us where we are today."
Meir said she hopes she and Koch provide inspiration "to everybody, not only women."
"To everybody that has a dream, that has a big dream and that is willing to work hard to make that dream come true, something that all of us that have made our way up here have done all throughout our lives," she said. "And I can tell you, the hard work certainly did pay off."
The remaining four astronauts aboard the International Space Station, all men, will stay inside while Koch and Meir complete their work.
People took to social media Friday to celebrate "HERstory in the making," as NASA is calling the history-making event.
Koch and Meir both joined NASA in 2013, the year NASA's astronaut class was 50% female. Koch is also on her way to making history with a 300-day mission, which will be the longest single spaceflight by a woman.