Nowacka was educated at the University of Warsaw, where she was active as a feminist in the Federation for Women and Family Planning. From 1997 to 2006, she was a member of the youth wing of Labour United and then of the party itself. In 2014 she stood unsuccessfully in the European elections in Lublin for Europa Plus, supported by Aleksander Kwaśniewski. She went on from that defeat to join Janusz Palikot's Your Movement, becoming a joint leader, and helped to create the United Left, a broad coalition. On 4 October 2015 she was named as its candidate for prime minister if it won the election,[3] and on 17 October she presented the coalition's programme at a conference in Katowice.[4] However, in the elections on 25 October the United Left failed to reach the 8 per cent threshold for obtaining parliamentary representation under Poland's system of election, while Nowacka herself failed to be elected in the Warsaw I parliamentary constituency.
The Polish elections of 2015 were unusual in that most of the major parties contesting them were led by women. While Nowacka was the leader of the United Left, Ewa Kopacz of the governing Civic Platform party was the incumbent prime minister, and Beata Szydło of the opposition Law and Justice party was the main challenger. In the event, Szydło was elected with an overall majority.[5]
In June 2019, Nowacka became leader of the political party Polish Initiative (iPL), which she originally founded as an association in 2016.[7] She is currently standing for election in Constituency № 26 (Słupsk) as a candidate for the Civic Coalition, of which iPL is a member party.
Nowacka has been fiercely critical of the influence that the Catholic Church has in Polish politics. When in October 2020 the Polish parliament considered placing stricter enforcement on abortion, Nowacka claimed that the Catholic bishops of Poland, the majority of whom strongly support such legislation, had "blood on their hands".[8] She later attended a protest against the new abortion restrictions, where she was tear-gassed by a police officer after approaching him and showing her ID card.[9]