The Shia ministers had suspended their participation on 12 December after the cabinet voted to call for an international tribunal to try suspects in the killing of former Lebanese prime minister Rafiq al-Hariri almost a year ago.
Talks to secure the five ministers' return faltered over their demand that the government declare Hizb Allah a resistance movement against Lebanon's arch-foe Israel, and not a militia, which would mean it must disarm according to a UN resolution.
"After the position taken by Prime Minister Fouad Siniora ... the leaderships of Hizb Allah and the Amal movement have decided to return their representatives to participation in the government meetings," senior Amal official and member of parliament Ali Hassan Khalil told a press conference on Thursday.
The joint announcement by pro-Syrian Hizb Allah and Amal, Lebanon's main Shia parties, is expected to ease a political crisis that has hobbled decision-making in the government and escalated into a public slanging match between politicians for and against the group keeping its weapons.
In comments to parliament earlier on Thursday, Siniora said Hizb Allah had always been considered a resistance organisation, but made no mention of the word militia.
"We have never called and will never call the resistance by any other name but the resistance and it is a national resistance and we will not use any other expression to describe it but national resistance," he said to applause.
"We have never called and will never call the resistance by any other name but the resistance"
Lebanese prime minister on the Hizb Allah
Hizb Allah, whose attacks were crucial in ending Israel's 22-year occupation of southern Lebanon in 2000, was the only Lebanese group to keep its arms after the 1975-1990 civil war.
It has been under increasing pressure to lay down its weapons since a UN Security Council resolution demanded that all foreign troops withdraw from Lebanon and militias disarm.
Syrian troops ended a 29-year military presence in Lebanon last year under international pressure and local protest following al-Hariri's murder, but Hizb Allah has kept its arms.
A unanimous UN Security Council renewed pressure on Lebanon late last month to disarm the group in line with the resolution issued in 2004.
The United States has long considered Hizb Allah a terrorist group while its ally, Syria, is a fixture on the US list of state sponsors of terrorism.