The 36-year-old Atlanta lawyer will be up against an empowered Republican majority. House Republicans added three seats in last week's election. Since then, three more Democrats have defected to the GOP caucus, meaning the party now has 111 seats in the 180-member chamber.
House Speaker David Ralston - who entered the chamber to congratulate Abrams after her election - suggested the GOP may not be done poaching from Democratic ranks.
"We're still in discussions with members of the other caucus and we'll see how it all shakes out," Ralston said.
Republicans need 120 members for a super majority, which would give them nearly unchecked power to move their agenda in the chamber by allowing them to approve constitutional amendments without Democratic support.
Abrams on Wednesday defeated Rep. Virgil Flood of Tyrone in a vote by secret ballot.
She replaces DuBose Porter of Dublin, who is leaving the House after an unsuccessful bid for the Democratic nomination for governor.
Abrams said she will work to hold the ruling GOP accountable.
"My job as minority leader is going to be to put sunshine on the legislation that's coming from this body, on the decisions that are being made and ensuring that every Georgian, every day, knows what's being done on their behalf," she said.
"And I think if they see what's happening, if they understand the consequences, they will vote Democratic."
The Democrats who have swapped to the GOP are state Rep. Alan Powell of Hartwell; Bob Hanner of Parrott; and Gerald Greene of Cuthbert.