The Constitutional Court in Karlsruhe on Wednesday overturned a 2010 ruling by the Federal Administrative Court that intelligence officers were right to have kept tabs on the Left party's Bodo Ramelow.
Ramelow had complained about the surveillance by the domestic intelligence officers from Germany's Office for Protection of the Constitution (BfV) around a decade ago, before he served for four years as a representative in the German national parliament, the Bundestag.
The surveillance was officially confirmed in 2006 when the BfV was ordered by a court in Thuringia to make its file on Ramelow public.
In its decision, the Constitutional Court said that such an encroachment - specifically the monitoring of a lawmaker - should only be possible in exceptional circumstances, where it met strict conditions of proportionality.
Officers are believed to have been suspicious of the politician's alleged links with the German Communist Party (DKP) during the 1980s.
However, the court found that there were no grounds to suspect Ramelow, said to be a moderate within the party, of wrongdoing.
The judges ruled that such surveillance should only be permissible "if there is an indication that the deputy has abused his mandate in the fight against the democratic constitutional order, or actively or aggressively fought against that order."
"I was spied on and snooped on for more than 30 years," said Ramelow, responding to the decision vie Twitter. "Now I hear that I have won a victory in Karlsruhe."
Ramelow is currently parliamentary group leader of the Left Party in the Thuringian state legislature.
rc/hc (AFP, dpa, Reuters)