In an interview from Riyadh with his party's Future TV, Hariri brushed aside rumours that he was under de facto house arrest in the kingdom, from which he announced his surprise departure.
"I am free here. If I want to travel tomorrow, I will," Hariri said.
"I will return to Lebanon very soon," Hariri said, adding later that he would land in Beirut "in two or three days".
Hariri, 47, announced he was stepping down from his post in a televised address on November 4 from Riyadh, and has yet to return to his native Lebanon.
However, Lebanese President Michel Aoun has yet to formally accept his resignation and said the premier has been "restricted" in his movements.
Hariri's surprise resignation came as tensions rise between Riyadh and Tehran, which back opposing sides in power struggles from Lebanon and Syria to Yemen.
At the time, Hariri accused Iran and its Lebanese ally Hezbollah of taking over his country and destabilising the broader region.
"We cannot continue in Lebanon in a situation where Iran interferes in all Arab countries, and that there's a political faction that interferes alongside it," he repeated on Sunday in apparent reference to rival movement Hezbollah.
"Maybe there's a regional conflict between Arab countries and Iran. We're a small country. Why put ourselves in the middle?"
Wearing a suit and tie and with a Lebanese flag in the background, the former premier looked tired on Sunday and spoke softly but firmly throughout the interview.
Hariri, who also holds Saudi citizenship, told journalist Paula Yaacoubian that he wrote his resignation himself and wanted to submit it in Lebanon, "but there was danger".
He also appeared to lay down an exit strategy, saying he would be willing to "rescind the resignation" if intervention in regional conflicts stopped.
"We need to respect the disassociation policy," Hariri said, referring to an agreement among Lebanese political factions that they would not interfere in Syria's six-year war.
He appeared to be alluding to Hezbollah's military intervention on behalf of the Syrian government, to which Hariri is opposed.
Hezbollah chief Hassan Nasrallah said Friday that Hariri was "detained in Saudi Arabia, he is banned from returning to Lebanon".
'Excellent' ties with Saudi
Hariri has spent the past week in a string of meetings with diplomats and Saudi officials in Riyadh, including an encounter with Saudi King Salman.
He left the kingdom once for a trip to Abu Dhabi.
In his interview on Sunday, Hariri said he has "excellent" ties with Crown Prince Mohammed bin Salman in an apparent effort to put to rest rumours that the Saudi crown prince had pressured him to step down.
"Really, I consider him a brother and he considers me a brother. It's an excellent and special relationship," he said.
But he refused to comment on the internal political turmoil in Saudi Arabia, where dozens of high-profile politicians and businessmen have been arrested in what authorities say is an anti-graft drive.
The two-time premier's father Rafik made his fortune in Saudi Arabia and also served as premier for years before he was assassinated in 2005.
Saad cited fears for his life when he resigned from his post last week, less than a year after his unity government was formed with Hezbollah.
Lebanese have expressed concern that the move could thrust the country into a political and economic tailspin, as it remains unclear who could replace Hariri.
Western countries moved quickly to express their support for the premier, with US Secretary of State Rex Tillerson calling him a "strong partner".
Tillerson warned against "any party, within or outside Lebanon, using Lebanon as a venue for proxy conflicts or in any manner contributing to instability in that country".
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)