Shinzo Abe’s Goal of Revising Japan’s Constitution Moves Closer After LDP Election Victory

Politicians on both sides said the election demonstrated the nation’s commitment to democracy after Mr. Abe, the longest-serving prime minister in Japanese history, was shot to death while campaigning in the city of Nara.

“We will not give in to this terrorism or be scared by it,” said Kei Sato, the candidate on whose behalf Mr. Abe had been speaking. Mr. Sato won his race and dispensed with the usual celebratory cheers.

The Liberal Democratic Party returned to power in 2012 under Mr. Abe’s leadership and has won every national election since then.

Revision of the constitution would require a two-thirds vote of both houses of Parliament followed by a popular referendum. The U.S.-written document, adopted in 1947, says Japan will never maintain war potential such as land, sea and air forces. The country nonetheless has a de facto military, called the Self-Defense Forces, which some scholars say is unconstitutional.

Mr. Kishida, who generally hasn’t made the issue a priority, said lawmakers should accelerate discussions about a revision that would make clear Japan’s military forces are legal. He also advocated strengthening government powers in emergencies such as a major earthquake.

“I think these are urgent matters,” Mr. Kishida said. “I want to concentrate efforts on putting together a specific proposal” that Parliament could submit for the national referendum, he said.

However, left-leaning opposition politicians said they would fight a revision that they said could entangle Japan in overseas wars. As Mr. Abe found during his long term in power from 2012 to 2020, the issue can be a divisive distraction when the nation faces economic challenges.

With all votes counted, Mr. Kishida’s LDP won more than half of the seats at stake in Parliament’s upper house, according to public broadcaster NHK. Combined with the seats held by the LDP’s coalition partner, a party called Komeito, the coalition will have 146 seats in the 248-seat chamber.

The LDP already holds a majority of the more-powerful lower house, which wasn’t up for election Sunday, as a result of its victory in an election last October.

The assassination of Mr. Abe on Friday jolted what had been a low-drama campaign. Authorities arrested a 41-year-old man, Tetsuya Yamagami, and said he was suspected of sneaking up behind Mr. Abe and firing a homemade gun at him. Mr. Yamagami told investigators he had problems with an organization that he believed was linked to the former prime minister and that led him to decide to kill Mr. Abe, police said.

Police didn’t publicly name the organization or describe why the suspect connected it to Mr. Abe. Japanese news organizations including the Asahi newspaper said it was a religious group and said Mr. Yamagami told authorities he was upset because he believed his mother had suffered financial difficulties while giving large donations to the group.

Custody of Mr. Yamagami was transferred to prosecutors from police on Sunday.

Secretary of State Antony Blinken, who has been on an Asia trip, will visit Tokyo Monday to offer condolences over Mr. Abe’s death, the State Department said.

Renho, a former opposition leader and current upper-house member who won re-election Sunday, said the ability of lawmakers on all sides to speak freely was the foundation of making the country better.

“We cannot allow pressure or violence to deprive politicians of their words—or of their lives,” said Renho, who goes by one name.

Prime Minister Kishida, who previously served as Mr. Abe’s foreign minister, spent Saturday much as he would any day before an election, hopping by train and plane to campaign in tight districts.

After the voting, he said: “There was great significance in the fact that we were able to carry through with this election” despite the shooting of Mr. Abe.

Vigorous retail campaigning has been a central part of Japanese politics since it adopted universal suffrage and enshrined parliamentary government in its U.S.-written constitution, adopted in 1947.

In the weeks before elections, candidates crisscross their districts giving speeches at train stations and shopping areas, typically with little or no security. Television advertising plays less of a role than in the U.S. because of rules limiting the type of ads candidates can run.

Write to Peter Landers at peter.landers@wsj.com