The runoff against Lt. Gov. Bill Halter came after a May 18 primary election in which neither Lincoln nor Halter managed to garner a majority of votes. Lincoln's 44.5 percent showing in that contest had experts predicting she would be the third senator to fall to a challenge from within their own party, The Washington Post said Tuesday.
With 91 percent of the vote counted, Lincoln maintained a 51.8 percent to 48.2 percent lead over Halter.
Organized labor poured more than $10 million into an attempt to defeat her, largely due to her opposition to the Employee Free Choice Act and the inclusion of the public option in healthcare reform legislation, the newspaper said.
Lincoln countered with a media blitz in the campaign's final days featuring former President Bill Clinton urging Arkansas voters to support her.
"This election is not about special interests, this election is not about me, this election is about us," Lincoln said in her victory speech.
In a bid for a third Senate term, Lincoln will face Republican candidate Rep. John Boozman in the November election.