Considered to be one of the most conservative Democrats in Congress, Lipinski narrowly beat progressive newcomer Marie Newman.
As of 5:30 a.m., Lipinski had 45,079 votes and Newman had 43,515 votes with 95.2 percent of the precincts reporting.
The close race was not called by the Associated Press until early Wednesday morning.
ABC7 reporter John Garcia said Lipinski spoke to the crowd, but did not declare victory, saying "the race was too close to call, but it looks good."
Wednesday morning, Newman released a statement saying in part, "After reviewing the results, we know that we lost by a thin margin. It was a good fight and I am so proud of the grassroots movement we built with hundreds of volunteers and partners all over the district. Since we started our campaign, Dan Lipinski has moved his position on healthcare, a path to citizenship, and the need for a fair minimum wage. We put him on notice that we expect better for all of the people in our district."
Lipinski is known as one of the most conservative Democrats in Congress. He's seeking his eighth term.
Newman has the backing of progressive groups and lawmakers, including U.S. Sen. Bernie Sanders and Chicago-area House members Jan Schakowsky and Luis Gutierrez. The district includes parts of Chicago's south and west sides and southwestern suburbs.
Both candidates were endorsed by unions, Lipinski by the AFL-CIO and AFSCME. Newman by the SEIU as well as a number of progressive groups.
Beauty shop owner Manuel Hernandez of Berwyn says he's going with Newman. The 46-year-old father says he doesn't think Lipinski "is enough of a Democrat."
Trucking company worker Joe Nowak of Summit says he voted for Lipinski because he's comfortable with him. He says Lipinski has been "a neighborhood figure my whole life."
Newman, a former advertising executive and mother of two, has accused Lipinski of being out of step with the values of the Democratic party and the 3rd Congressional District.
Lipiniski is one of the rare members of his party who is anti-abortion, opposes same-sex marriage and voted against the Affordable Care Act. His positions have caused two other Democratic members of Congress from Illinois -- Jan Schakowsky and Luis Gutierrez -- to endorse Newman.
However, Lipinski is supported by the most powerful Democrat in the state, Illinois House Speaker Michael Madigan, which is a hurdle that Newman knows she must overcome.
The Associated Press contributed to this report.