Lew said that Jackson will remain on the back of the bill and Alexander Hamilton will stay on the front of the $10 bill.
Lew also announced changes to the $5 bill and the $10 bill. The $5 bill will retain the President Lincoln portrait on the front, but will feature Martin Luther King, Jr., Marian Anderson, and Eleanor Roosevelt on the back to honor events that have taken place at the Lincoln Memorial.
The back of the $10 bill will feature pivotal figures from the women's suffrage movement: Lucretia Mott, Sojourner Truth, Susan B. Anthony, Elizabeth Cady Stanton, and Alice Paul.
"The decision to put Harriet Tubman on the new $20 was driven by thousands of responses we received from Americans young and old," Lew wrote in an open letter posted on Medium.com. "I have been particularly struck by the many comments and reactions from children for whom Harriet Tubman is not just a historical figure, but a role model for leadership and participation in our democracy."
Lew said that the upgraded $10 note will be the first to be redesigned and places into circulation, but that he directed the Bureau of Engraving and Printing to accelerate the redesign of the $20 and $5. He expects the new designs to be unveiled in 2020.
Tubman was born into slavery, but escaped to Philadelphia in 1849, and provided valuable intelligence to Union forces during the Civil War.
The group Women on 20s, issued a statement saying: "After more than a year of campaigning to convince the U.S. Treasury to replace the portrait of Andrew Jackson on the $20 bill with the face of a female American hero, Women On 20s is ready to claim victory, but only if Secretary Lew commits to issuing the new $20 bill alongside the $10 by 2020."
Lew announced last year that he was considering replacing Hamilton on the $10 bill with a woman. That ran into strong objections from Hamilton supporters. Some credit the popularity of the Broadway smash hit "Hamilton" for helping save the bill.
When will the new $20 bill be released?
You could be waiting a long time. If the Treasury Department stays on its current release schedule, the $20 bill's redesign won't happen until 2030. But as Lew said in his statement, the redesign could be accelerated.