On 9 November 1989 the Berlin Wall fell, borders between East and West Germany were reopened and on 1 December 1989 the Volkskammer abrogated the constitutional provisions that gave the SED a monopoly of power in the GDR.

[16] This empowered a younger generation of reform politicians in East Germany's ruling socialist class, who looked to Soviet President Mikhail Gorbachev's glasnost and perestroika as their model for political change.

[17] Reformers like authors Stefan Heym and Christa Wolf and attorney Gregor Gysi, lawyer of dissidents like Robert Havemann and Rudolf Bahro, soon began to re-invent a party infamous for its rigid Marxist–Leninist orthodoxy and police-state methods.

In the 1994 federal election, in spite of an anti-communist "Red Socks" campaign by the then-ruling Christian Democrats aimed at scaring off eastern voters,[25] the PDS increased its vote to 4.4%.

In the 1998 federal election, the party reached the high-water mark in its fortunes by tallying 5.1% of the national vote and 36 seats, thus clearing the critical 5% threshold required for guaranteed proportional representation and full parliamentary status in the Bundestag.

The party's future seemed bright, but it suffered from a number of weaknesses, not the least of which was its dependence on Gysi, considered by supporters and critics alike as a super-star in German politics who stood in stark contrast to a colourless general membership.

After the 2002 debacle, the PDS adopted a new programme and re-installed a respected moderate, long-time Gysi ally Lothar Bisky, as chair.

Its electoral base in the eastern German states continued to grow, where it ranked with the CDU and SPD one of the region's three strong parties.

However, low membership and voter support in Germany's western states continued to plague the party on the federal level until it formed an electoral alliance in July 2005 with Labour and Social Justice – The Electoral Alternative (WASG), a leftist faction of dissident Social Democrats and trade unionists which had split away from the SPD some months prior, with the merged list being called the Left Party.

After marathon negotiations, the PDS and WASG agreed on terms for a combined ticket to compete in the 2005 federal election and pledged to unify into a single left-wing party in 2006 or 2007.

Gregor Gysi, returning to public life only months after brain surgery and two heart attacks, shared the spotlight with Lafontaine as co-leader of the party's energetic and professional campaign.

A gaffe by Lafontaine, who described "foreign workers" as a threat in one speech early in the campaign, provided ammunition for charges that the Left was attempting to exploit German xenophobia.

The Left Party suffered serious losses in the 2006 elections for the city-state government of Berlin, losing nearly half of its vote and falling to 13%—slightly ahead of the Greens.

Berlin's popular Social Democratic mayor, Klaus Wowereit, nevertheless decided to retain the weakened party as his coalition partner.

The PDS had experience as a junior coalition partner in two federal states—Berlin and Mecklenburg-Western Pomerania—where it co-governed until 2006 with the Social Democratic Party of Germany (SPD).

After German reunification, leading members of the PDS were frequently suspected of having connections to East Germany's secret police, the Stasi (State Security Service).

[26] At about the same time, the media revealed that Lutz Heilmann, a Left Party Bundestag deputy from the state of Schleswig-Holstein, had worked for several years for the Stasi.

Though Heilmann had served as a bodyguard, not as an informant or secret police officer, he violated a Left Party regulation obliging candidates to reveal Stasi involvement.

Charges of a Stasi past were also a factor in the Bundestag's decision to reject Lothar Bisky as the Left Party's candidate for the post of parliamentary vice president.

In the Saxony, the chairman of the Left Party group, Peter Porsch, faced losing his mandate in the Saxon parliament because of his alleged Stasi past.