Koch and Meir ventured out into the vacuum of space at 7.38 a.m. EDT (5.08 p.m. India time) for the space walk, according to NASA.
It is the first time that all space walkers are women and the 43rd space walk to include women.
This is Koch's fourth space walk and Meir's first.
The space walk is the 221st in support of station assembly, maintenance and upgrades and the eighth outside the station this year.
An all-women space walk, involving Koch and NASA astronaut Anne McClain, was originally scheduled for March.
But that was scuttled because properly fitted spacesuits could not be readied in time for both astronauts, Space.com reported.
So far, the 15 women who have conducted a space walk did so with a male companion.
The first all-women space walk is a milestone worth noting as NASA looks forward to putting the first woman and next man on the Moon by 2024 with the agency's Artemis lunar exploration programme.
Space walks are not easy. Astronauts typically describe them as the most physically challenging thing they do.
"In the end, I do think it's important, and I think it's important because of the historical nature of what we're doing. In the past women haven't always been at the table," Koch was quoted as saying by NASA when asked in an interview about the importance of conducting her mission and the first all-female space walk.
Koch and Meir went out into the vacuum of space to replace a battery charge/discharge unit that failed to activate after new lithium-ion batteries were installed on the space station's exterior structure on October 11.
The unit is one of several that regulate the charge put into the batteries collecting energy from the station's solar arrays. Though the unit's failure has not affected station operations or crew safety, it does prevent the new batteries from providing increased station power, NASA said.
( With inputs from IANS )