The move is in step with an August government pledge to release all political detainees. The amnesty may be aimed at garnering support for the government while peace talks with the main southern rebel group are ongoing in Kenya.
“He has just been released,” PNC official Muhammad al-Amin Khalifa told Reuters by telephone from Khartoum, saying al-Turabi was on his way to his residence in the Sudanese capital.
An official Sudanese source also confirmed the report.
Al-Turabi was arrested in February 2001 for crimes against the state, following a power struggle with Sudanese President Umar Hasan al-Bashir.
In mid-August, press reports said al-Bashir's Islamist government extended al-Turabi's detention for six months.
Once the president's chief ideologue, al-Turabi was a key figure in the Islamist government set up by al-Bashir after a coup in 1989.
He was arrested after signing a deal with the rebel Sudan People's Liberation Army, which has been fighting since 1983 for greater autonomy in the mainly Christian and animist south.