Ali ani al-Harzi, a reported member of al Qaeda with ties to the group's Africa terror cell, was released by Tunisian authorities after being detained since last March on terrorism charges, according to his lawyer, Anouar Awled Ali.
A justice ministry spokesman confirmed the release of al Harzi to Reuters, but did not comment on the terms of his release.
His release ends a months-long standoff between Washington and Tunis over al Harzi, an issue that briefly became a political flashpoint in the larger debate over the Obama administration's handling of the consulate strike in Benghazi, Libya.
Al-Harzi, identified as a key suspect in the terrorist attack in Benghazi, was handed over to Tunis shortly after his arrest in Turkey last October, according to news reports at the time.
FBI investigators had requested access to al-Harzi at the time of his arrest, in the hopes of gaining more information into the circumstances leading up to the deadly assault in Libya, which left four Americans dead, including U.S. Ambassador Christopher Stevens.
The White House remains under fire for its changing accounts of the Sept. 11 attack, initially claiming the strike was the result of an anti-U.S. protest run amok.
U.S. intelligence and defense officials later admitted the strike was a terrorist attack, but noted the raid was an opportunistic assault and not a coordinated or pre-planned attack by Islamic terror groups in the country.
Sen. Lindsey Graham (R-S.C.) is threatening to hold up John Brennan's confirmation as the new head of CIA over unanswered questions regarding the consulate attack.
Tunisian officials initially denied the FBI's request to interrogate al-Harzi but later granted American investigators access to the suspect.
Tunis only approved the interrogations after a number of congressional Republicans, including Graham and Sen. Saxby Chambliss (R-Ga.), pressured Tunisian diplomats in Washington to do so.
Both lawmakers heralded the agreement as a "welcome breakthrough" in the ongoing U.S. investigation of the consulate strike in a joint statement last November.
"We hope our interview of [al-Harzi] will bear fruit and we can bring to justice those responsible" for the consulate attack, they added at the time.
But with al-Harzi's release, U.S. officials remain no closer to identifying the perpetrators of the Benghazi raid.
At the time of his arrest, al-Hazri was reportedly en route to Syria, to fight alongside other Islamic militant groups participating in the ongoing civil war between anti-government rebels looking to overthrow longtime President Bashar Assad.