Edwards has acknowledged that investigators are looking into his presidential candidate finances. Sources say they want to know if payments made by the former senator's campaign to Hunter violated federal law.
Edwards has admitted to having an affair with Hunter after meeting her during his failed presidential bid. Her video production company was paid $114,000 by his political action committee to produce campaign videos.
In February 2008, Hunter gave birth to a baby girl. There is no father listed on the child's birth certificate. Edwards adamantly denied in an interview with ABC News last summer that he fathered the child with Hunter, and he welcomed a paternity test.
His wife, Elizabeth, has said while promoting a book that she doesn't know if her husband is the father.
Former Edwards' aide Andrew Young, who made an appearance in Raleigh while the grand jury was sitting last month, claimed to be the child's father in 2007, but hasn't spoken publically since.
Why Hunter brought her child to the grand jury Thursday isn't clear. A federal source told Eyewitness News the child was not subpoenaed.
Exactly what investigators want to know from Hunter is also unknown. Grand jury proceedings are secret, and the U.S. attorney's office in Raleigh has declined to confirm or deny an investigation.
Edwards has said his affair with Hunter ended in 2006. That year, his political action committee paid Hunter's video production firm $100,000 for work. Then the committee paid another $14,086 on April 1, 2007.
Edwards has said there was nothing wrong with the payments.
"I am confident that no funds from my campaign were used improperly," he said in a statement to reporters earlier this year. "However, I know that it is the role of government to ensure that this is true.