A military plane carrying Hamdi landed at 1 p.m. local time (6 a.m. ET) in Riyadh, Frank Dunham Jr. said. Hamdi's case led to ato indefinitely hold enemy combatants.
Dunham said he talked with Hamdi by telephone just after the plane landed Monday, and said Hamdi told him he felt "awesome."
Hamdi will be not be charged with any crime under an agreement negotiated by his lawyer and the Justice Department. The agreement requires Hamdi to give up his American citizenship, renounce terrorism and not sue the U.S. government over his captivity.
Dunham said he would sign papers on Monday to dismiss the case and turn them over to government lawyers. Officials with the U.S. Justice Department did not immediately return a phone call seeking comment early Monday.
Hamdi was born in the southern state of Louisiana in 1980 to Saudi parents and raised in Saudi Arabia. He was captured on a battlefield in Afghanistan in late 2001 during the fight against the Taliban regime.
He contends he never fought against the United States and that he had been trying to get out of Afghanistan when he was captured.
After his capture, Hamdi was taken to the U.S military base at Guantanamo Bay, Cuba, then transferred to a Navy brig in Norfolk when officials realized he was a U.S. citizen. He then was moved to a Navy brig in Charleston, S.C. He spent his captivity in solitary confinement.
The Supreme Court ruled in June that Hamdi and others like him could not be held indefinitely without seeing a lawyer and getting a chance to contest their incarceration in court. That led to the negotiations for Hamdi's release.
Hamdi was originally set to be flown to Saudi Arabia on Sept. 26. The flight from Charleston was delayed because of bad weather and the need to work out unanticipated details with the Saudi government, said Dunham, a federal public defender based in Virginia.
"Sometimes when you've got to do diplomatic things with other countries, people don't do everything when you want them to," he said.
The only other U.S. citizen being held in the South Carolina military prison is "dirty bomb" suspect Jose Padilla, a former Chicago gang member. His case is still pending in lower courts.
Dunham said he was frustrated that the fight over Hamdi's case took 2 1/2 years, but pleased with the final outcome.
"It feels wonderful because we had fought to get the victory in the Supreme Court, but it really didn't mean anything until we got Mr. Hamdi released."
The Justice Department agreed not to ask the Saudi government to detain Hamdi. Officials have said Hamdi no longer poses a threat to the United States and no longer has intelligence value.
The release agreement requires Hamdi to notify Saudi officials if he becomes aware of "any planned or executed acts of terrorism."
Hamdi agreed to live in Saudi Arabia for five years and not travel outside that country during that time. He must never travel to Afghanistan, Iraq, Israel, Pakistan or Syria.
In addition to the enemy combatants it has jailed in the United States, the Bush administration also holds several hundred terrorism suspects at Guantanamo Bay. The Supreme Court also ruled this summer that those suspects must be given some form of court hearing.
The hearings have begun, but many detainees are boycotting them because they are not allowed a lawyers. A handful of detainees also face military tribunals for alleged war crimes.