The victory means that the hawkish former Prime Minister Shinzo Abe will get a second chance to lead the nation after a one-year stint in 2006-2007. He would be Japan's seventh prime minister in six-and-a-half years.
Public broadcaster NHK's exit polls projected that the LDP, which ruled Japan for most of the post-World War II era until it was dumped in 2009, won between 275 and 300 seats in the 480-seat lower house of parliament. Official results were not expected until Monday morning. Before the election, it had 118 seats.
The results were a sharp rebuke for Prime Minister Yoshihiko Noda's ruling Democratic Party of Japan, reflecting widespread unhappiness for its failure to keep campaign promises and get the stagnant economy going during its three years in power.
With Japan stuck in a two-decade slump and receding behind China as the region's most important economic player, voters appeared ready to turn back to the LDP.
A serious-looking Abe characterized the win as more of a protest vote against the DPJ than a strong endorsement of his party.
"I think the results do not mean we have regained the public's trust 100 percent. Rather, they reflect `no votes' to the DPJ's politics that stalled everything the past three years," he told NHK. "Now we are facing the test of how we can live up to the public's expectations, and we have to answer that question."
The ruling Democrats, which won in a landslide three years ago amid high hopes for change, captured less than 100 seats, exit polls indicated, down sharply from its pre-election strength of 230.
Calling the results "severe," Noda told a late-night news conference he was stepping down to take responsibility for the defeat.
"I apologize deeply for our failure to achieve results," he said. "It was the voters' judgment to our failure to live up to their expectations during our three years and three months of leadership."
The LDP will stick with its long-time partner New Komeito, backed by a large Buddhist organization, to form a coalition government, party officials said. Together, they will probably control about 320 seats, NHK projected – a two-thirds majority that would make it easier for the government to pass legislation.
Noda said a special parliamentary session would be held before year-end to pick a new prime minister. As leader of the biggest party in the lower house, Abe will almost certainly assume that post.
The new government will need to quickly deliver results ahead of upper house elections in the summer. To revive Japan's struggling economy, Abe will likely push for increased public works spending and lobby for stronger moves by the central bank to break Japan out of its deflationary trap.
Still, some voters said they supported the LDP's vows to build a stronger, more assertive country to answer increasing pressure from China and threats of North Korean rocket launches. Abe has repeatedly said he will protect Japan's "territory and beautiful seas" amid a territorial dispute with China over some uninhabited islands in the East China Sea.
"I feel like the LDP will protect Japan and restore some national pride," Momoko Mihara, 31, said after voting for the Liberal Democrats in the western Tokyo suburb of Fuchu. "I hope Mr. Abe will stand tall."
The LDP may also have benefited from voter confusion over the dizzying array of more than 12 parties, including several news ones, and their sometimes vague policy goals.
One of the new parties, the right-leaning, populist Japan Restoration Party, won between 40 to 61 seats, NHK projected. The party, led by the bombastic nationalist ex-Tokyo Gov. Shintaro Ishihara and Osaka Mayor Toru Hashimoto – both of whom are polarizing figures with forceful leadership styles – could become a future coalition partner for the LDP, analysts said.
Ishihara was the one who stirred up the latest dispute with China over the islands when he proposed that the Tokyo government buy them from their private Japanese owners and develop them.
In this first election since the March 11, 2011, earthquake, tsunami and nuclear disasters, atomic energy ended up not being a major election issue even though polls show about 80 percent of Japanese want to phase out nuclear power.
In the end, economic concerns won out, said Kazuhisa Kawakami at Meiji Gakuin University.
"We need to prioritize the economy, especially since we are an island nation," he said. "We're not like Germany. We can't just get energy from other countries in a pinch."
The staunchly anti-nuclear Tomorrow Party – which was formed just three weeks ago _captured between six and 15 seats, NHK estimated.
Tomorrow Party head Yukiko Kada said she was very disappointed to see LDP, the original promoter of the nuclear energy policy – and still the most pro-nuclear party – making a big comeback.
Abe, 58, is considered one of the more conservative figures in the increasingly conservative LDP.
During his previous tenure as prime minister, he pursued a nationalistic agenda pressing for more patriotic education and upgrading the defense agency to ministry status.
It remains to be seen how he will behave this time around, though he is talking tough toward China, and the LDP platform calls developing fisheries and setting up a permanent outpost in the disputed islands, called Senkakus by Japan and Daioyu by China – a move that would infuriate Beijing.
During his time as leader, Abe also insisted there was no proof Japan's military had coerced Chinese, Korean and other women into prostitution in military brothels during Japan's wartime aggression in Asia. He later apologized but lately has suggested that a landmark 1993 apology for sex slavery needs revising.
He has said he regrets not visiting Yasukuni Shrine, which enshrines Japan's war dead, including Class-A war criminals, during his term as prime minister. China and South Korea oppose such visits, saying they reflect Japan's reluctance to fully atone for its wartime atrocities.
The LDP wants to revise Japan's pacifist constitution to strengthen its Self-Defense Forces and, breaching a postwar taboo, designate them as a "military." It also proposes increasing Japan's defense budget and allowing Japanese troops to engage in "collective self-defense" operations with allies that are not directly related to Japan's own defense.
It's not clear, however, how strongly the LDP will push such proposals, which have been kicked around by conservatives for decades but usually make no headway in parliament because they are supported only by a fairly small group of right-wing advocates.
"The economy has been in dire straits these past three years, and it must be the top priority," Abe said in a televised interview. "We must strengthen our alliance with the U.S. and also improve relations with China, with a strong determination that is no change in the fact the Senkaku islands are our territory."