The retired four-star general is set to testify in a closed-door session on Friday.
Wednesday, lawmakers are expected to be briefed by both the FBI and CIA on what both agencies currently know about the situation. They will try to prove that politics was not involved.
Also Wednesday, President Barack Obama answered questions about the scandal in his first post-election news conference. He said he is withholding judgment on the timing of the revelations that Petraeus was under investigation for a possible national security violation.
Officials have said that Obama was not told about the investigation until after the election. He says he has "a lot of confidence generally" in the FBI, which is conducting the inquiry.
Meantime, new information is coming out about the affair that forced Petraeus to resign as the head of the CIA.
ABC News reports that Paula Broadwell, Petraeus' mistress and biographer, has admitted to taking classified documents from government buildings. As a former intelligence officer, she had clearance to do so, but she could now face criminal charges.
Also entangled in the controversy is Petraeus' replacement in Afghanistan, Gen. John Allen.See timeline of the Petraeus-Broadwell affair
Allen is accused of sending thousands of emails to Tampa socialite Kill Kelley. It's believed the vast majority of emails between Kelley and Allen were not romantic in nature - but did contain pet names like "sweetheart" and "dear." Both are married.
Kelley is the one who alerted the FBI about threatening emails, which were traced back to Broadwell. It was during this investigation that FBI agents learned of the affair between Petraeus and Broadwell. The FBI says Broadwell and Petraeus exchanged thousands of emails, many salacious in nature. They believe she sent Kelley threatening emails because she was jealous of her.
Kelley recently called 911 from her home to complain about all the reporters on her front lawn. She requested diplomatic protection due to her status as an unofficial social ambassador for some of the military's top brass.
"I'm an honorary consul general so I have inviolability, so they should not be able to cross my property. I don't know if you want to get diplomatic protection involved as well now because that's against the law to cross my property since this is now like, you know, it's inviolable," Kelly says in the 911 recording.
Allen had been nominated to become the next commander of U.S. European Command and the commander of NATO forces in Europe, but the appointment has been put on hold at Defense Secretary Leon Panetta's request. Instead, Allen could face charges of adultery, which is a crime under the Uniform Code of Military Justice. Allen, 58, has denied wrongdoing.
At a news conference Wednesday in Australia, Panetta said, "No one should leap to any conclusions," and said he is fully confident in Allen's ability to continue to lead in Afghanistan. He added that putting a hold on Allen's European Command nomination was the "prudent" thing to do.
The Associated Press and ABC News contributed to this report.