The scathing opinion, written by Anne Arundel Circuit Court Senior Judge Lynne A. Battaglia, marks a massive victory for two GOP-backed lawsuits against the state's congressional maps.
The legislature passed that map and overrode a veto from Republican Gov. Larry Hogan late last year. The map got an "F" from the Princeton Gerrymandering Project and has the potential to eliminate Maryland's last Republican congressman.
"The 2021 Congressional Plan in Maryland is an ‘outlier,’ an extreme gerrymander that subordinates constitutional criteria to politician considerations," Battaglia wrote.
The opinion said that "the right for all votes of political participation in Congressional elections, as protected by Article 7 [of the Maryland Constitution], was violated by the 2021 plan."
"The voice of Republican voters was diluted and their right to vote and be heard with the efficacy of a Democratic voter was diminished," it added. "The 2021 Congressional Plan is unconstitutional, and subverts the will of those governed."
Battaglia scheduled a hearing for April 1 at 9 a.m. to consider whether a new map drawn by the legislature complies with the Maryland Constitution and Declaration of Rights.
Hogan's group Fair Maps is behind the lawsuit, which was consolidated with a separate one by Tom Fitton's Judicial Watch.
Hogan set up a commission to propose an alternative map to the one the state legislature adopted. That commission would have set up congressional districts that could have led to two GOP U.S. House members representing the state.
The governor lauded the decision as a "historic milestone" for the state Friday.
Battaglia ordered the state legislature to redraw the state's congressional maps by March 30. It is possible that the ruling could be appealed to the Maryland Court of Appeals, which is the state's highest court. But that court is made up primarily of justices appointed by Hogan, which gives Hogan allies confidence that Battaglia's ruling will stand.
If the legislature does not come back with a map that's satisfactory to Battaglia or the Court of Appeals, it's not clear exactly what further remedies are available to the Maryland courts.
In other states that had intractable gerrymandering disputes, courts ended up drawing the congressional districts. That was the case in Pennsylvania just last month amid a dispute between the GOP-controlled legislature and Democrat Gov. Tom Wolf.
The eventual congressional district lines that are implemented will remain in effect until the next Census in 2030.