Judge Robert Hyatt's ruling makes Coffman's suburban Denver district more Democratic by incorporating all of Aurora, Colorado's third largest city.
It also moves Republican-leaning portions of Coffman's district into the eastern plains seat held by Republican U.S. Rep. Cory Gardner.
Republicans have held Coffman's 6th Congressional District for decades.
Both parties filed lawsuits after the state Legislature failed to agree on new district lines this spring to reflect population changes.
The map proposed by state Democrats makes minor changes to Denver's 1st Congressional District, the 3rd Congressional District in western and southern Colorado, and the 5th Congressional District surrounding Colorado Springs, said Mark Grueskin, an attorney representing the Democrats.
Republicans had argued for minor changes to district lines that were adopted 10 years ago.
"I think that we presented the only map that really reflected the changes in Colorado," Grueskin said. "The other map, in part, or in whole, embraced the Colorado of 2001."
Grueskin said he expects Hyatt's decision to be appealed but called it "sound and extremely defensible."
Republican Party Chairman Ryan Call did not immediately return a call for comment.
(Copyright 2011 by The Associated Press. All Rights Reserved.)