After completing his compulsory military service (as common soldier but as Munitions Systems specialist Conscript) in the Swedish Air Force at the Jämtland Air Force Wing (F 4) airbase 1976–77, Löfven began his career in 1978 as a welder at Hägglunds in Örnsköldsvik. Two years later, he was chosen as the group’s union representative, and went on to hold a succession of union posts. In 1995, he started as an employed ombudsman in the Swedish Metalworkers’ Union, working in the areas of contract negotiations and international affairs. In 2001, he was elected vice-chairman of the Metalworkers’ Union; in November 2005 was elected as the first chairman of the newly formed trade union IF Metall.

Löfven has been a member of the Social Democrats since the age of 13 and was active in SSU, the youth league, in his teens. Löfven was elected to the executive board of the Social Democrats in 2006, shortly after becoming chairman of trade union IF Metall.

Löfven led his party through the 2014 European Parliament election where the Social Democrats retained their position as the largest party from Sweden in the European Parliament. However, the election results at 24.19% was a slightly inferior result than the result in the 2009 European Parliament election; the party’s seats in the European Parliament was reduced from six to five and the party’s results was the lowest in an election at the national level since universal suffrage was introduced in 1921.

Löfven led his party through the 2014 general election, which resulted in a hung parliament. Their election result of 31.0%, up from 30.7%, was slightly better than the result in the 2010 general election, but the result was also the party’s second worst result in a general election to the Riksdag since universal suffrage was introduced in 1921.

In January 2012, following the resignation of Håkan Juholt, it was reported that Löfven was being considered as his successor. On 26 January 2012 the executive board nominated Löfven to become the party’s new leader. On 27 January 2012, Löfven was elected Leader in a party-room ballot. Löfven was confirmed as party leader at the party’s bi-annual congress on 4 April 2013.

He announced that he would form a minority coalition government consisting of his own party and the Green Party. On 2 October 2014, the Riksdag approved Löfven to become Prime Minister, and he took office on the following day, alongside his Cabinet. The Social Democrats and the Green Party voted in favour of Löfven becoming Prime Minister, while close ally the Left Party abstained. The opposition Alliance-parties also abstained while the far-right Sweden Democrats voted against.

The Government’s first budget was introduced to the Riksdag on 23 October 2014. The Left Party, which had been given influence over the budget, supported it; however, the non-socialist coalition, the Alliance, introduced a competing budget to the Riksdag on 10 November, as they had promised prior to the 2014 election, and the Sweden Democrats also introduced their own budget on the same day.

In his Policy Statement, introduced to the Riksdag on 3 October 2014, Löfven said that his Government would recognise the State of Palestine. On 30 October 2014 the Government, through Minister for Foreign Affairs Margot Wallström, announced that the Government had decided to officially recognize the State of Palestine and explained the recognition by saying that it is the only solution to get to a two-state solution between Israel and the State of Palestine. Sweden is the first country within the European Union to do so after gaining membership (with other members, such as Poland, withholding recognition previously issued under Communist rule). Israel called the move unconsidered and Israel recalled its ambassador, Isaac Bachman, following the recognition. Bachman returned to Sweden on 29 November 2014. In December 2015, Löfven caused outrage in Israel by claiming that stabbing attacks are not considered terrorism by international standards; he later revised his comment, explaining that it is now known that the stabbing attacks are sanctioned by some terror organisations.

According to Riksdag practice, the parties support their own budget and if their budget falls they abstain from voting in the second round. However, on 2 December, the far-right Sweden Democrats announced that, after their own budget fell in the first voting round, they would support the Alliance parties’ budget in the second voting round, thus giving that budget a majority in the Riksdag. This caused a crisis for the newly-elected Government, which was exacerbated after their own budget was voted down by the Alliance parties and the Sweden Democrats on 3 December. Löfven immediately announced that he would call an early election, to be held on 22 March 2015.

On 22 December, sources within the Riksdag leaked information that the Government was negotiating with the Alliance parties (the Moderate Party, Centre Party, Liberal People’s Party and the Christian Democrats) to find a solution and to avoid a fresh election. On 27 December, the Government and the Alliance parties held a joint press conference where they announced that the six parties had reached an agreement designed to ensure that the Government’s budgets would be voted through in the second round of voting. The agreement was dubbed “Decemberöverenskommelsen” (December Agreement), was called historical by Löfven and was agreed to remain in force until the 2022 election, regardless of the results of the 2018 election. Subsequently, Löfven announced that he no longer intended to call a snap election. The centre-right Alliance withdrew from the agreements in 2015, but allowed the minority government to continue governing.

In 2015, when a rising number of refugees and migrants began to make the journey to the European Union to seek asylum, Europe was hit by a migrant crisis and Sweden received over 150,000 refugees in 2015.

During the autumn of 2015, the reception of refugees increased significantly to over 80,000 in two months and with terror group Islamic state rampage in the Middle East and the following attacks in Paris in November 2015, the Löfven cabinet significantly reverted Sweden’s migration policy. On 23 October 2015, a bipartisan migration agreement was signed between the cabinet parties and the oppositional Moderate Party, the Centre Party, the Liberals and the Christian Democrats which included, among many other changes, temporary residency permits, total financial support requirements for family reunification and by law forcing municipalities to help with sheltering refugees in order to better distribute the burden across the country.

On 12 November 2015, the cabinet introduced temporary border controls with immediate effect. The cabinet also proposed identity checks for every individual passing the Danish–Swedish border and closing of the Öresund Bridge, giving up the latter on 8 December 2015 after severe criticism. On 17 December 2015, the Riksdag passed legislation to introduce identity checks with the votes 175 in favor, 39 against and 135 abstained. On 4 January 2016, the identity checks was introduced, which means that people who can not show a valid identity card, license or passport are not allowed to cross the border into Sweden, breaking with the Nordic Passport Union for the first time since 1954. Only twelve hours later the Danish Prime Minister Lars Løkke Rasmussen announced that Denmark will implement temporary border controls along the German–Danish border with immediate effect as a consequence of Sweden’s identity checks.

In July 2017, it became known to the public that Maria Ågren, a former Director-General of the Swedish Transport Agency, had been investigated after having cleared confidential information threatening the security of the country. The act was made in connection with a procurement of IT services with a non-governmental company in 2015. Among the cleared data were wanted vehicles, armored vehicles, the entire Swedish vehicles register, Swedish company secrets, the Swedish police criminal record- and suspicion registers, the Swedish state’s internal security system and information about agents within the Swedish Military Intelligence and Security Service.

Several days after it first became public, Löfven held a press conference on 24 July 2017 where he said that “there’s been an accident at the Transport Agency”. Responsible cabinet minister Anna Johansson said she had been aware of the situation since January 2017 and blamed her former state secretary Erik Bromander for not having informed her earlier. Cabinet ministers Anders Ygeman and Peter Hultqvist were reported to have been aware of the situation since the beginning of 2016, but chose not to inform the head of government.

Löfven visited Iran in February 2017 and held talks with Ali Khamenei to improve economic relations.

However, on 25 September 2018, the Riksdag approved a motion of no confidence against Löfven with a 204–142 vote. Löfven remained in office as head of a caretaker government. While it initially looked as though the Alliance would be able to form a government, the Alliance’s leaders subsequently failed to secure enough votes or abstentions to replace him.

After a record-long period of government formation, Löfven was eventually re-elected as Prime Minister on 18 January 2019, after an agreement was struck between the Social Democrats, Greens, Liberals, and Centre Party, with the Left Party agreeing to abstain from voting against Löfven. As a result, the minority coalition government of the Social Democrats and Green Party was reformed. The second Löfven Government was sworn in on 21 January.