Her decision to step down followed a turbulent series of events that saw her budget fail to pass through parliament before the junior Greens Party announced it was leaving the coalition government.
“There is a constitutional practice that a coalition government should resign when one party quits,” Andersson, a Social Democrat, told reporters.
“I don’t want to lead a government whose legitimacy will be questioned.”
Andersson said she hoped to be elected to the position again soon as the head of a minority government made up of only the Social Democrats.
Wednesday’s crisis began when the Centre Party withdrew its support for Andersson’s budget, due to the concessions made to the Left. That meant the new PM’s budget didn’t have enough votes to pass in parliament.
Lawmakers instead adopted an alternative budget presented by the opposition conservative Moderates, Christian Democrats and far-right Sweden Democrats.
The right-wing’s opposition budget – negotiated jointly by the conservative Moderates and Christian Democrats, and the Sweden Democrats – had won with 154 votes to 143.
The fatal blow came when Greens leader Per Bolund said his party could not tolerate the opposition’s “historic budget, drafted for the first time with the far-right”, and quit the government.
The Greens slammed the approved budget, describing it as “differentiating between people, butchering the environmental budget, and increasing emissions”, referring to the new budget’s lowered petrol and diesel tax – a reduction of 50 öre per litre from May 1st 2022.
Bolund stated at a press conference that it is “not the Green Party’s goal to carry out a budget negotiated by the Sweden Democrats,” and that they “cannot sit in a government on a budget negotiated by the Sweden Democrats”.
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Andersson had been set to formally assume her duties on Friday after a meeting with King Carl XVI Gustaf, after being approved by parliament in a separate vote on Wednesday morning.
Speaker of parliament Andreas Norlen said he had accepted Andersson’s resignation and would contact party leaders before deciding Thursday how to proceed.
The exact steps of what will happen next are not entirely clear.
The Green Party did say that it would support Magdalena Andersson in another prime minister vote if it comes to that. This may mean that Andersson will eventually become prime minister anyway, if none of the party’s change their stance on supporting her bid.
The rules for a budget vote and a prime minister vote differ slightly in Sweden. In a budget vote, the proposal with the most yes votes wins. In a prime minister vote, the candidate wins as long as a majority does not vote against them.
This means that Andersson will need no more from the Centre Party than its abstentions in a second prime minister vote – this would be enough to make her PM, provided the Left Party and the Green Party also abstain or vote in her favour, which they likely will.