The statue, also the only one of a child in the Capitol collection, depicts Keller at her home in Tuscumbia, Ala., as her teacher Anne Sullivan spelled out the word "water" in her hand while pumping water over her other hand.
Keller said the moment "awakened (her) soul" to the potential for her life. She later became an internationally celebrated advocate for those with disabilities. She died in 1968.
In a ceremony unveiling the statue in the Capitol Rotunda, Alabama Gov. Bob Riley said the monument will remind people "that courage and strength can exist in the most unlikely places."
"Children especially need to be reminded of this basic truth, and this statue will get their attention," he said of the millions of children who visit the Capitol.
House Speaker Nancy Pelosi said Keller laid the groundwork for laws such as the Americans with Disabilities Act. She said the statue shows "that people must be respected for what they can do rather than judged by what they cannot."
Each state has two statues in the Capitol as part of the National Statuary Hall Collection, which was permanent until 2000, when Congress allowed for changes.
The Keller statue replaces one of Jabez Curry, a former Confederate officer, educator, ambassador and preacher who was once well known for advocating for free public education.
Riley, a former congressman, came up with the idea to replace Curry when he found that most Alabama visitors didn't know who Curry was.
The Keller statue was funded with private donations raised by the state and will be placed in the new Capitol Visitor Center. The project cost about $325,000.
The statue of Curry, who died in 1903, will be moved to Samford University, near Birmingham.