The two men were forced into the same district when Louisiana lost a congressional seat because of anemic population growth in the latest federal census. The state will have six U.S. House seats in the new term that begins in January.
Boustany, a retired doctor from Lafayette, will represent the 3rd District covering southwest Louisiana and Acadiana in Congress.
"We're glad to get this done," he said Saturday night. "This looks like a very solid victory. We had a very strong ground game, which was a key element in the runoff. We reached out to a lot of voters with a solid message backed by the results I've gotten in Congress."
The race had been attack-heavy, since both men ran as conservative Republicans opposed to the policies of President Barack Obama and had little philosophical ground in which to distinguish themselves.
The district design favored Boustany, a traditional Republican candidate allied with House Speaker John Boehner. Landry, a freshman congressman, was the tea party favorite, but he was unable to build enough grassroots support to oust Boustany.
Pearson Cross, chairman of the political science department at the University of Louisiana-Lafayette, said Boustany was the "de-facto incumbent" throughout the race.
"Most voters in the district have voted for Charles Boustany, think he's done a good job, are comfortable with him," Cross said.
Though they had three other challengers in the November election, the two congressmen had campaigned as though it was a two-man race since the election sign-up period in August.
Boustany described his GOP opponent as a good ol' boy politician who would say anything to get elected, habitually skipped votes in Congress and spread distortions about Boustany's record to distract voters from his own lack of accomplishments.
Landry criticized Boustany as lacking the courage to make tough votes for his district and instead following in lockstep with Washington Republican leaders even if south Louisiana voters didn't support the policy.
The race was one of Louisiana's most expensive congressional contests, with nearly $6 million spent between the two men and even more from outside groups. Boustany had a significant edge in fundraising, raising nearly $2 million more than Landry, according to the most recent campaign finance reports filed with the Federal Election Commission.
Republican Gov. Bobby Jindal didn't make an endorsement in the race.
Also in Saturday's election, Republican appeals court judge Jeff Hughes won the runoff for an open seat on the Louisiana Supreme Court representing the eight-parish Baton Rouge region.
The seat is vacant because Chief Justice Catherine "Kitty" Kimball is retiring at the end of January.
Hughes, a former state District Court judge from Livingston Parish, defeated one of his colleagues for the position: John Michael Guidry, a Democrat and former lawmaker from Baton Rouge.
Hughes broke with the usual approach that many judges take when running for office. Instead of refusing to weigh in on hot-button topics, Hughes branded himself a conservative and touted his beliefs as being "pro-life, pro-gun and pro-traditional marriage."
He'll be sitting on a high court expected to face headline-grabbing challenges in the upcoming year, including a decision on whether the financing for Jindal's state-funded private school tuition program is unconstitutional.
By MELINDA DESLATTE, Associated Press