The general had been summoned to Washington to testify in several closed-door hearings this week on the deadly September 11 attack on the US consulate in Benghazi, Libya, prior to his sudden resignation last week.
The sudden scandal, in which investigators discovered Petraeus had an affair with a military reservist who wrote his biography, had thrown his participation into question.
"General Petraeus as you know will be testifying before the intelligence committee," McCain told reporters on Wednesday in a Senate studio, adding afterwards that the general's participation would be on Thursday.
Democratic Senator Dianne Feinstein, chair of the Senate Select Committee on Intelligence, told CNN she expected Petraeus would agree to testify at a later date, adding that she had seen nothing to link the sex scandal to Benghazi.
A close McCain ally, Senator Lindsey Graham, also said Petraeus had indicated he would appear before the intelligence committee, but did not provide a date.
"That's likely to be in a classified setting," Graham said. And he added that other senior national security officials, notably Defense Secretary Leon Panetta, would likely be called to testify before the Senate Armed Services Committee.
US media have reported that Petraeus would testify to Congress on Friday.
Lawmakers from both parties, and from the Senate as well as the House of Representatives, have clamored for Petraeus and others to speak at various classified hearings to learn more about the circumstances of the attack which killed US ambassador Christopher Stevens and three other Americans.
Republicans have called for investigations into what happened in Benghazi and why President Barack Obama's administration has offered a shifting narrative of events after initially insisting that the attack stemmed from a protest against an anti-Islam video.