Urpilainen was a member of Parliament for the Vaasa constituency from the 2003 national elections.[6] In parliament, she was a member of the Committee on Education and Culture and a deputy member of the Finance Committee. In addition to her parliamentary work, she was also a member of the Advisory Council of the Finnish Institute of International Affairs.
After the 2011 parliamentary election, in which the SDP became the second-largest party, Urpilainen was appointed Minister of Finance and Deputy Prime Minister in the cabinet led by Jyrki Katainen.[9] In this capacity, she also chaired the meetings of the Nordic Council Ministers of Finance in 2012.
The surge of the eurosceptic True Finns party in the 2011 elections sparked a move from the Social Democrats under Urpilainen to toughen their stance on the euro significantly, leading Finland to become the only country to demand collateral from Greece and Spain as part of their international rescues.[10] On 6 July 2012, Urpilainen said the following on her website: "Finland would prefer to consider leaving the Eurozone rather than to pay other countries' debts in the currency area."[11] International news media, such as The Daily Telegraph, misinterpreted the statement as a threat that Finland would leave the eurozone. Urpilainen's assistant Matti Hirvola later clarified her statements and that she had meant that Finland did not wish to be responsible for paying other countries' debt deposits.[12] Only one month later, Urpilainen had to revise the government's growth target for that fiscal year down to zero as exports slowed; the only Eurozone countries that fared worse were Greece and Portugal.[13]
Urpilainen sought another term as party chair in the Social Democratic Party's 2014 party conference in May. She was narrowly defeated by her challenger, Antti Rinne, in a 257 to 243 vote.[14] Urpilainen subsequently stepped down as the Minister of Finance in June.
Ahead of the 2018 presidential elections, Urpilainen was widely mentioned as a potential candidate.[15] By February 2017, she announced she would not seek the presidency.[16]
On 16 August 2023, the chairman of the Social Democratic Party Sanna Marin asked Urpilainen to run in the 2024 Finnish presidential election as the party's candidate.[19] After months of consideration, Urpilainen announced her candidacy in November 2023.[20] In the election, she received 4.34% of the total vote count and failed to advance to the second round of voting.[21]