The White House also reiterated the importance of the accord and Lee's trip.

"This establishment of a new economic partnership will create jobs and economic growth here in the U.S. as well as in Korea,"

Press Secretary Jay Carney said at a press briefing. "This is a very important and significant state visit. It comes at a time that's really a high point in the bilateral relationship and in our alliance with South Korea."

The two sides launched free trade talks in 2006 and struck a deal a year later.

The administrations of Lee and Obama had additional negotiations on the accord, signed by their predecessors, in 2010 and reached a supplementary deal on the new terms of auto trade.

Obama has openly expressed hope for South Koreans to drive more American vehicles.

The U.S. FTA with South Korea is the largest trade deal since the U.S. agreed to the North American Free Trade Agreement (NAFTA) in the early 1990s.

South Korean officials expect the country's parliament to follow suit in the near future so that the trade pact can go into effect as early as in January.

Experts hailed the U.S. passage of the FTAs as a rare bipartisan achievement and one of the major accomplishments of Lee's visit.

"In terms of the economic agenda per se, I think the free trade agreement was the main accomplishment, as it was clearly accelerated to try to get it through both houses of Congress before the president's visit," Edward Alden, a researcher at Council on Foreign Relations said. "This was one potential deadline."

Richard Bush, senior analyst at the Brookings Institution, said it may be also Obama's biggest achievement in the remainder of his current term.

"Given how few political agreements are possible in Washington these days, this may be the biggest achievement in the last two years of President Obama's current term, particularly if there is stalemate in the budget negotiations," he said.