Mr Lee campaigned for the presidency on a platform of economic change
South Korea's ruling conservative party has won an overall majority by a narrow margin in parliamentary elections.
Early results from the National Election Commission show the Grand National Party (GNP) has won at least 153 seats in the 299-seat legislature.
The victory is a boost for the new President Lee Myung-bak and will make it easier for him to pass his wide-ranging economic reforms.
Official figures show voter turnout was a record low of 46%.
This was partly due to voter fatigue, reports the BBC's John Sudworth in Seoul, but also to the disarray in the GNP, which has been mired in factional infighting for the first months of Mr Lee's presidency.
Latest figures show Mr Lee's GNP party took 131 local district races, and another 22 seats in party-list proportional voting.
They also show that the liberal United Democratic Party (UDP), previously the largest party in the national assembly, has secured 81 seats. It had been hoping for 100 seats.
Smaller parties and independents will share the remaining seats.
GNP leader Kang Jae-sup said people had voted for them in the hope of "national unity and revitalising the economy".
The parliamentary polls come little more than three months after Mr Lee's victory in a hard-fought presidential election.
Mr Lee campaigned on a platform of economic reform and revitalisation - but needed control of parliament to pass the changes. He also promised a tougher stance on North Korea.
"I believe the opinion of the people will be well reflected in this election, which will help our nation's development," he said as he cast his vote.
At a polling station in Seoul's Bangbae district Kang Hyo-Shik, 33, told news agency AFP he voted for the GNP "so that the president may push through with a drive to reactivate the economy".