Walid Jumblatt, the Lebanese Druze leader, has met with Bashar al-Assad, the Syrian president in Damascus, sealing a process of reconciliation between the former foes.
The meeting helps to consolidate Syria's political gains in Lebanon as it attempts to restore influence lost when it withdrew troops from its neighbour five years ago under international pressure.
It also opens channels with Lebanese politicians who have been firmly in the US-backed camp.
Jumblatt turned fiercely anti-Syrian after the 2005 assassination of Rafiq al-Hariri, the former Lebanese prime minister, and blamed al-Assad for the killing.
"The meeting discussed the importance of role of the resistance as a guarantee against Israeli plans," Syria's offcial news agency said, in reference to the Lebanese group Hezbollah, which mediated the meeting.
Since his war of words against Syria, Jumblatt has said good ties with Syria were now crucial to preventing Lebanon descending into chaos and to preserve his minority Druze community.
Thabet Salem, a leading Syrian journalist and commentator, said the meeting could help internal cohesion in Lebanon, after UN investigators sought to question six Hezbollah members about the killing of al-Hariri.
He said: "There might be strong pressure coming on Hezbollah relating to the al-Hariri affair, and consolidating the internal front is crucial to deal with any problem."
A special international court set up in The Hague has yet to indict anyone for al-Hariri's killing, in which Damascus and Hezbollah have denied any role.
Jumblatt had warned that the aftermath of the al-Hariri assassination could ignite sectarian bloodshed between Sunnis and Shia in Lebanon.
In an interview with Al-Jazeera earlier this month, Jumblatt said that critical comments he had made about al-Assad were "inappropriate".
Wednesday's talks in the Syrian capital followed meetings between Jumblatt and Syria's allies in Lebanon, including Hassan Nasrallah, the leader of Hezbollah, who led efforts to help melt the ice between Jumblatt and Syria.
Although other anti-Syrian politicians have already started changing their tone toward Damascus, Jumblatt's overtures to al-Assad left him with critics in Lebanon.
Ghassan Tueini, owner of a leading Arab publishing house, said the al-Hariri killing in 2005 "brought out the human being in Jumblatt," but his rapprochement with Syria "returned him to being a [mere] politician".
After the al-Hariri killing, Jumblatt spearheaded the strategy of the US and Saudi-backed "March 14" alliance, which accused Syria of the killing.
He was also one of the strongest critics of Syrian and Iranian-backed Hezbollah, and its operations outside the control of the sectarian-based Lebanese state.
Hezbollah and its pro-Syrian allies fought Jumblatt's followers in a 2008 conflict that brought Lebanon to the brink of renewed civil war, but their relations have since improved.
Al-Hariri killing sparked international criticism that forced an end to Syria's 29-year military presence in Lebanon.
Syria has been regaining influence in Lebanon since then, helped by its emergence from Western isolation and a subtler approach to Lebanese politics and ties with Beirut.