Michel Aoun, a Maronite Christian and staunch foe of Syria, was charged in 1990 with assaulting state security, national unity and the constitution, as well as embezzling state funds.
But a court ruled on Wednesday that he was exempt from those charges by an amnesty law that cleared the bloody records of Lebanese politicians after the 1975-1990 civil war.
Many Maronites say the arrest of Christian former militia leader Samir Geagea and the exile of Aoun symbolise the targeting of their community by the Syrian-dominated order after the war.
With Syria formally ending its 29-year military and intelligence presence in Lebanon last week, Aoun said he would return from exile in Paris on 7 May.
Lebanese prosecutors will examine separate charges against Aoun on Thursday over some comments he made about Syria's influence.
Forced into exile
Aoun, who has strong support among some Lebanese Christians, has said members of his Free Patriotic Movement would contest the parliamentary elections due to begin on 29 May.
Former Lebanese president Amin Gemayel appointed Aoun to head a military cabinet in 1988 but pro-Syrian Muslims rejected his appointment as prime minister, a position traditionally reserved for a Sunni Muslim.
Aoun's supporters have long
campaigned for his return
Aoun was forced into exile a year after Syrian forces crushed his rebellion and ended the Lebanese civil war in 1990.
Aoun's supporters, who have put up posters announcing his return, stepped up calls for him to come back after the 14 February assassination of former prime minister Rafiq al-Hariri boosted demands for the Syrians - who many Lebanese blamed for the killing - to pull out.
Anti-Syrian opposition lawmakers are also proposing an amendment to the amnesty law that would free Geagea, whose supporters protested outside parliament on Wednesday.