The win is an endorsement of the Liberal Democratic Party's "Abenomics" programme, which has helped spark a tentative economic recovery in Japan.
It's also a vindication for Abe, who lost upper house elections in 2007 during his previous stint as Prime Minister.
"We've won the public's support for decisive and stable politics so that we can pursue our economic policies, and we will make sure to live up to the expectations," Abe told public broadcaster NHK after he was projected to win based on exit polls and early results.
The victory also offers the hawkish Abe more leeway to advance his conservative policy goals, including revising the country's pacifist constitution and bolstering Japan's military, which could further strain ties with key neighbors China and South Korea, who are embroiled in territorial disputes with Japan.
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Controlling both houses of Parliament has been an elusive goal for Japanese governments in recent years.
With a divided Parliament, it has been hard to pass legislation, and voters fed up with the gridlock and high leadership turnover appeared willing to opt for the perceived safety of the LDP, which has ruled Japan for most of the post-World War II era.
"Now that we got rid of the twisted parliament, the LDP is going to face a test of whether we can push forward the economic policies so that the people can really feel the effect on their lives," Abe told NHK.
Japan's stagnant economy is showing signs of perking up, helped by the aggressive monetary and fiscal stimuli that Abe has implemented since he took office in late December.
Stocks have surged, business confidence is improving and the weaker yen has put less pressure on vital exporters.