[3] Miller started his political career as an activist of the Socialist Youth Union, where he held the position of Chairman of the Plant Board, soon becoming a member of the Town Committee.

[5] After graduation, Miller worked at the PZPR Central Committee, supervising the Group, and later on the Department of Youth, Physical Education and Tourism.

In December 1999, at the Founding Congress of the Democratic Left Alliance (SLD), he was elected its Chairman, holding the function continuously until February 2004.

After revealing that affair in 1991, Włodzimierz Cimoszewicz called Miller to abstain from taking an MP's oath due to accusations laid against him.

Miller played an important role in concluding the case of Colonel Ryszard Kukliński, for which he was severely criticised within his political circle.

A similar disapproval was expressed after Miller’s support for the Concordat and the candidature of Leszek Balcerowicz to the position of President of the National Bank of Poland.

Following the victory of the Left (41% vs. 12% of the subsequent party) in the Parliamentary Election in 2001, on 19 October 2001, President Aleksander Kwaśniewski appointed Miller Prime Minister and obliged to nominate the government.

During his term, the unpopular program of cuts in public expenses was implemented, together with a hardly successful reform of health care financing.

The reforms of the tax system and of the Social Insurance Institution were continued, and the attempt to settle the mass-media market failed.

On 13 December 2002, at the summit in Copenhagen (Denmark), Prime Minister Leszek Miller completed the negotiations with the European Union.

[8] On 16 April 2003 in Athens, Miller, together with Cimoszewicz, signed the Accession Treaty, bringing Poland into the European Union.

Miller’s government, in collaboration with various political and social forces, organized the accession referendum with a successful outcome.

Already in 2002, Miller gave permission to the U.S. government to run a secret CIA prison at Stare Kiejkuty military training center, three hours north of Warsaw.

[13] On 1 May 2004, together with President Kwaśniewski, he was in Dublin, taking part in the Grand Ceremony of the accession of 10 states, including Poland, to the European Union.

In 2005, despite the support of the Łódź Branch of the Democratic Left Alliance, Miller was not registered on the election list to the Parliament.

After the election, Miller became active in journalism, writing mainly for the “Wprost” weekly on liberal economic concepts and current political issues.

In the first half of 2005, he stayed at the Woodrow Wilson International Center for Scholars in Washington, D.C., implementing a research project: “Status of the new Poland in the Eastern Europe’s space”.