Lt. Ridge Alkonis, a Navy officer who was imprisoned in Japan after killing two members of a Japanese family in a car crash, was on his way to the United States on Wednesday after a yearslong diplomatic effort to bring him home, Biden administration officials said.

Lieutenant Alkonis, 35, was released from prison after serving half his sentence for negligent driving. Under the terms of the International Prisoner Transfer Program, set in place by a treaty between the United States and Japan, he was likely to continue serving his sentence in the United States, administration officials said.

The length of his incarceration will be set by the U.S. Parole Commission, an independent part of the Justice Department, officials said. The commission could reduce his sentence or allow him to serve part of it in home confinement. Lieutenant Alkonis will remain in detention in the United States until the commission makes its decision.

The case involving Lieutenant Alkonis, a sailor stationed at the Yokosuka naval base, south of Tokyo, was set in motion in May 2021, when the minivan he was driving near Mount Fuji careened into the parking lot of a noodle restaurant, killing two people.

The fallout since the accident has strained diplomatic ties between Japan and the United States, with Lieutenant Alkonis’s family and supporters insisting that he had suffered from altitude sickness and been denied due process in a foreign court system that gave little weight to his guilty plea and repeated apologies.

In Japan, however, Lieutenant Alkonis is widely viewed as a criminal whose actions took two innocent lives. The court, which found that he had fallen asleep after driving while drowsy, followed the wishes of the victims’ family to impose a “severe penalty” in the case, sending the American to prison for three years.

Officials said President Biden was personally involved in discussions that led to the lieutenant’s release. But the officials described the conversation as highly sensitive because the president and his top aides did not want to insult the Japanese government by suggesting that they did not respect the country’s judicial system and need for accountability.

The family of Lieutenant Alkonis mounted a long campaign to bring him home. Members of Congress joined the effort, arguing that he had a medical emergency while driving and should not be held culpable for the deaths that resulted.

In a statement, the family thanked the Biden administration and expressed optimism that Lieutenant Alkonis would be released after the review of his case in the United States.

“After 507 days, Lt. Ridge Alkonis is on his way home to the United States. We are encouraged by Ridge’s transfer back to the United States but cannot celebrate until Ridge has been reunited with his family,” the family said in the statement to The Associated Press. “When the Biden administration is presented with the complete set of facts and circumstances surrounding the case, we’re confident they will promptly recognize the absurdity of Ridge’s conviction.”

Senator Mike Lee, Republican of Utah, has led the effort to demand the sailor’s return. He has repeatedly threatened to push for a rethinking of the U.S.-Japan military cooperation agreement if the country did not allow Lieutenant Alkonis to return.

“If you transfer Lieutenant Alkonis back to the U.S. before midnight on Feb. 28, 2023, we will do our best to forget that this whole thing never happened,” Mr. Lee wrote in February. “It will be hard, but we will try.”

Administration officials said that Mr. Biden, Vice President Kamala Harris and Jake Sullivan, the national security adviser, personally worked with Japanese officials to secure the lieutenant’s return. Mr. Biden raised the issue with Prime Minister Fumio Kishida of Japan during a visit to the White House in January.

But U.S. officials said the release was not negotiated the way it would have been for a hostage exchange with an adversary. Instead, the details of Lieutenant Alkonis’s release — and what will happen to him in the United States — were strictly determined by the prisoner transfer treaty and the U.S. laws establishing it.

The program, which began in 1977, was devised to facilitate the rehabilitation of prisoners, which is often difficult when they are detained in other countries, where they do not speak the language, officials said. Transfers are made only with the agreement of both countries and of the prisoner.

Two weeks ago, after the two governments reached agreement, a U.S. official traveled to Japan to obtain consent from Lieutenant Alkonis and make sure he understood the terms.

The officials said the Biden administration had offered to provide information to the Parole Commission about Lieutenant Alkonis’s service record and anything they requested. But the officials stressed that by law, neither the White House nor Justice Department officials had any role in the commission’s decision.

The officials also said the United States had not exchanged prisoners or provided anything in return to Japan.

The decision to bring back Lieutenant Alkonis did not change his conviction in Japan, officials said, and it did not mean the Biden administration was challenging the conclusions of the court there.

Since taking office, Mr. Biden has instructed his national security team to focus on bringing home Americans who are detained abroad. In most cases, that has involved people who are designated as “wrongly detained” by adversaries. Those included Brittney Griner, an American basketball player who was detained in Russia; five Americans who had been imprisoned in Iran; and several oil executives who had been detained in Venezuela.

Officials said several prisoners have also been transferred back to the United States from more friendly countries.