[2] The predecessor of Fortum was Imatran Voima (IVO), which was founded in 1932 to operate the Imatrankoski hydroelectric power plant in Imatra.

It was created from the merging of Imatran Voima and Neste Oy, the Finnish national oil company.

[10] In 2012, Fortum shared the number one position in the Carbon Disclosure Project's Nordic climate index.

[16] In September Fortum signed an agreement with Rosatom and British Rolls-Royce Engines to develop nuclear power.

[citation needed] In 2016, Fortum acquired Grupa DUON S.A, an electricity and gas sales company in Poland, and Ekokem Corporation, a leading Nordic circular economy company specialised in material and waste recycling, final disposal solutions, soil remediation and environmental construction.

[24] In 2020 Fortum and Kværner informed that they would cooperate on a Carbon capture and storage project for waste incineration at Klemetsrud energigjenvinningsanlegg.

The German state-owned KfW bank will provide Uniper with additional liquidity support as required until this EUR 8 billion capital increase is completed.

At that point, change of control clause in the financing agreement will be triggered and the buyer will provide the financing for the redemption of Fortum's EUR 4 billion shareholder loan granted to Uniper and the release of the EUR 4 billion parent company guarantee.

[citation needed] The parties have also agreed that Fortum will have a right of first offer in case Uniper intends to divest all or parts of its Swedish hydro and nuclear assets until the end of 2026.

Fortum considered the decision illegal and wrote off assets from the balance sheet, recording a loss of 1.7 billion euros.

[33] In February 2024 Fortum launched arbitration proceedings against Russia, seeking compensation for its assets seized by Russian authorities.

[41] Extinction Rebellion Finland accused Fortum for greenwashing for continuing and scaling up its fossil fuel business, for example opening (through Uniper) Dateln4 coal-fired power plant in Germany in 2020 and suing the Netherlands on the basis of the Energy Charter Treaty for banning coal.

[citation needed] In February 2014, Fortum equipped three schools with solar-powered infrastructure in Bhilwara, India, where they had a solar plant.