US State Department spokesman Richard Boucher on Thursday said 24-year-old Corporal Wassef Ali Hassoun had been picked up in Beirut after making contact, but gave few details.
"We were able to go get him this morning," Boucher told reporters in Washington. "He made contact with us."
US embassy spokeswoman Elizabeth Wharton said Hassoun had been accompanied by family members.
"The priority will be on repatriation back to the US but as for the schedule I'll leave that to the Defence Department," said Wharton.
Hassoun contacted US officials
A US defence official at the Pentagon said: "He appears to be healthy. We're working through the details of what the next steps are."
In another twist to the story, two people were killed and several were wounded when a gunbattle erupted near the home of Hassoun's family in northern Lebanon, witnesses said.
Members of his family traded fire with another family who taunted them by referring to Hassoun and his relatives as US agents, said the witnesses.
The area is a stronghold of deeply religious Sunni Muslims with strong clan ties. Blood feuds among rival families are not uncommon.
Hassoun, who joined the US military after emigrating to the United States from Lebanon four years ago, had been missing from his unit in Iraq since 21 June.
Hassoun's family exchanged fire
with another causing chaos
Statements on Internet sites used by Islamists said he had been taken hostage and then beheaded, but his family - who urged his captors to spare him as an Arab and Muslim - said this week he had been released and was safe.
A relative of Hassoun's in Tripoli said the marine was now at the heavily fortified US embassy complex in the hills overlooking Beirut's coastline.
"Wassef is at the US embassy," Abd al-hamid Hassoun told reporters.
The US military has declined to comment on media reports that Hassoun deserted from his unit, but a Marine Corps spokesman said a criminal investigation into Hassoun's disappearance was under way. He gave no details.
Hassoun, a linguist from the First Marine Expeditionary Force, also has family in West Jordan, Utah.
"He appears to be healthy"
Unnamed US defence official
Conflicting statements by different groups on the Internet fuelled confusion over his fate.
Lebanon's Foreign Ministry at one point confirmed reports of his death before withdrawing its statement.
Later, an Islamist group said he had been moved to safety after pledging to leave the US military.