For the first time in more than a century, a woman is coming to a U.S. currency bill, the Treasury Department announced Wednesday. In a process that has been "years in the making," the government will unveil the new $10 bill in 2020, and it will include a famous female face, Treasury Secretary Jack Lew said on a call with reporters. The department has not yet decided which woman will grace the new bill, he said, but the eventual choice will hold global significance. "With such a wide reach, America's currency makes a statement about who we are and what we stand for as a nation," Lew said, adding that "this decision of putting a woman on the $10 bill reflects our aspirations for the future as much as a reflection of the past."

Some have called for a woman to replace Andrew Jackson on the $20 bill, but Lew said that note was not yet up for a redesign. One group, Woman on 20s, announced in May that abolitionist Harriet Tubman had won its campaign to be the new face of that bill.

This won't be the first time a woman was on U.S. currency: Martha Washington and Pocahontas both had places on bills in the 1800s. Still, the new $10 note will be the first to feature a woman in more than 100 years, Lew said.

The current $10 bill features Alexander Hamilton, and fans of the founding father need not worry about his outright disappearance. The Treasury will "definitely" continue to include his image in some way on the new notes, Lew said—whether that be on the same bill as the as-yet-undecided woman, or on a different bill. Read MoreWomen on 20s aims to put a feminine face on a bill

"It was personally very important to me to make sure that as we make this decision we continue to honor Alexander Hamilton, who played such a formative role in the creation of our country, the establishment of democracy as we know it, and the principle of the soundness of our currency," Lew said. In fact, the range of options remains fairly unrestricted, the treasury secretary said, explaining that his department could even opt to include more than one woman.