A majority of the justices ruled that the 2011 redistricting "clearly, plainly and palpably" violated the state Constitution and moved Monday to throw out the old map, which it said unfairly benefited Republicans.
That replacement plan must then be fowarded to Governor Tom Wolf, who is required to submit it to the court by February 15th.
The new map will not be used for the special election to replace disgraced GOP ex-Rep.
Last week, the nation's highest appellate court blocked a lower court's order for North Carolina to redraw its congressional lines.
In a 4-3 vote, the Democratic-led judiciary struck down the boundaries of the state's 18 congressional districts.
The suit, originally brought by the League of Women Voters, contended that "in 2011 Pennsylvania elected officials manipulated the congressional district boundaries to entrench a Republican delegation in Congress and minimize the ability of Democrats voters to elect U.S. House representatives".
Unlike other recent gerrymandering decisions, the U.S. Supreme Court can not overrule or stay this ruling, because it was not a federal question, but rather a state court interpreting a state constitution. The court is expected to rule by the end of June in both cases.
The court gave lawmakers just 2 1/2 weeks to redraw all 13 of their congressional districts, though the U.S. Supreme Court agreed to pause that timeline, which means the GOP-drawn lines could be in effect in November's midterms.
Congressional districts must consist of compact and contiguous territory that do not divide any county, city, municipality or ward, except when needed to ensure districts have equal populations, the court's order says. It's possible Democratic Gov. Tom Wolf could veto the new map, which would put the job of refiguring it in the court's hands.
Earlier this month, Pennsylvania Lt. Governor Mike Stack, a defendant in the case, proposed a new map that was drawn using nonpartisan algorithms.
A proposal that would begin the process for a change to the state constitution to create an independent commission to draw the maps has stalled in the Legislature.
"I strongly believe that gerrymandering is wrong and consistently have stated that the current maps are unfair to Pennsylvanians", Wolf said in a statement.
Monday's decision could encourage similar state-court challenges elsewhere, said Li, the redistricting expert. The court's order did not specify how the map runs afoul of the law but said a full opinion will be released in the future.