The independent peace movement in the GDR was a reaction to two political developments: the arms race between the superpowers and the continuing militarisation of GDR society, as manifest in the 1978 incorporation of military instruction as a compulsory part of school curricula, for instance. When female conscription became a possibility under new legislation governing military service in 1982, Poppe and some other women drew up a petition protesting the new legislation and collected signatures. This initiative gave rise to the formation, also in 1982, of “Women for Peace” (Frauen für den Frieden), which remained one of the most important opposition groups outside of the Church up through to the Peaceful Revolution. Its members worked against the militarisation of society, called for disarmament on both sides and for democracy and human rights in the GDR.

On 12 December 1983, Ulrike Poppe and Bärbel Bohley were arrested by the Ministry for State Security (Ministerium für Staatssicherheit, MfS) on suspicion of “the treasonous disclosure of information” (§99 of the GDR Criminal Code). Protests against their arrest broke out within and outside of the GDR. A broad wave of solidarity took shape. The MfS held out for six weeks, but then bowed to the pressure and released the two “Women for Peace” activists.

In 1976, the MfS launched operation “Zirkel”, within which Ulrike Poppe and her husband were kept under observation and persecuted. It was one of the most extensive operations ever planned by State Security. Ulrike Poppe was the target of social/psychological “decomposition” measures (Zersetzung) over the course of many years, as well as frequent detentions and fines. The MfS considered her to be part of the small hard core of implacable enemies of the SED regime.

She was a co-founder of the most important opposition group of the 1980s, the Initiative for Peace and Human Rights (Initiative Frieden und Menschenrechte, IFM) as were Gerd Poppe, Wolfgang Templin, Bärbel Bohley, Reinhard Weißhuhn, Peter Grimm, Ralf Hirsch, Werner Fischer, Antje und Martin Böttger and others. This group resolutely spoke out for democracy, freedom, human rights and the rule of law and engaged in a continuous dialogue with the opposition in East Europe and with non-governmental organisations, politicians and journalists in the West. Unlike some IFM members, Ulrike Poppe engaged in numerous talks and discussions with SED members and officials. She wanted to be sure that both her own thoughts and other ideas being discussed in society were getting through to them. At the same time, she expressed her views in samizdat publications and signed a plethora of petitions, proclamations, open letters and announcements by the opposition.

In 1987, Poppe was chosen to represent the Berlin-Brandenburg region in the “continuation committee” of “Frieden konkret”, a GDR-wide network of opposition groups and grassroots church groups. Starting in 1987, she was also active in a working group at the Bartholomäus (St. Bartholomew) congregation in Berlin that addressed the rejection of exclusion in practices and principle. Hans-Jürgen Fischbeck, Stephan Bickhardt, Konrad Weiß and Wolfgang Ullmann were among those participating in the discussions of this group. In 1989, this initiative gave rise to the civic movement Democracy Now (Demokratie Jetzt, DJ); Ulrike Poppe was one of the original signatories of its founding proclamation that September. Democracy Now was one of the motors of the Peaceful Revolution in 1989. In this period, Poppe served in its speakers' council and, along with Wolfgang Ullmann, participated at the Central Round Table, which met from December of 1989 to March of 1990. She subsequently joined the staff of the Alliance 90/The Greens parliamentary group in the Volkskammer.

After German reunification, Poppe worked as director of studies at the Evangelical Academy of Berlin Brandenburg, organising events on contemporary history and political topics in this capacity. Poppe was never interested making a profession out of her political activism. Her voice is heard in public debate in a variety of forms; particularly worth mentioning in this respect are her efforts to advance the understanding of the Communist dictatorships and address their injustices, to promote international networking in this area and to ensure compliance with and respect for human rights. In her capacity as Brandenburg's state commissioner charged with dealing with the consequences of the Communist dictatorship (Landesbeauftragte zur Aufarbeitung der Folgen der kommunistischen Diktatur, LAkD) from 2009 to until 2017, Poppe was able to demonstrate an approach that was important to her during her activism in the opposition as well: seeking understanding across the boundaries of political parties and ideologies, exchanging perspectives and opinions through discourse. Unlike in the past, she no longer had to fear that doing so would result in harassment, arrest or her expulsion from the country. Thus the courage she displayed over many years has paid off, and the hopes she kept alive for many years have been, at least partially, fulfilled.