[7] On 7 November 2023, Costa resigned following an investigation involving members of his government in connection with alleged corruption and malfeasance in handling lithium mining and hydrogen projects in the country.

Costa stayed as Prime Minister in a caretaker capacity until his successor, hitherto leader of the opposition Luís Montenegro, was sworn in on 2 April 2024.

[15] Costa graduated from the Faculty of Law of the University of Lisbon in the 1980s when he first entered politics and was elected as a Socialist deputy to the municipal council.

[22] Costa narrowly lost the mayoral race to the Unitary Democratic Coalition (CDU) candidate by a 35 to 34 percent margin.

[23] In the 1996 presidential election, António Costa was the campaign director of Jorge Sampaio's successful run for the Presidency of the Republic.

[20] During the 2003 Casa Pia child sexual abuse scandal, António Costa's name was involved in wiretaps where he appears to want to interfere with the Public Prosecutor's Office to avoid the arrest of the PS deputy Paulo Pedroso.

[27] Costa resigned as an MEP on 11 March 2005 to become Minister of State and Internal Administration in the government of José Sócrates following the 2005 national elections.

[28] António Costa resigned from all government offices in May 2007 to become his party's candidate for the municipality of Lisbon, Portugal's capital city.

[33] Also, he pledged to roll back a hugely unpopular hike in value added tax on restaurants and reinstate some benefits for civil servants.

[31] On 4 October 2015, the conservative Portugal Ahead coalition that had ruled the country since 2011 came first in the elections winning 38.6% of the vote, while the Socialist Party (PS) came second with 32.3%.

[37] In October 2017, the opposition People's Party (CDS) launched a motion of no-confidence in Costa's government over its failure to prevent the loss of human lives in the lethal Iberian wildfires, the second such disaster in four months; the motion was largely symbolic as the minority Socialist government continued to be backed in parliament by two left-wing parties.

[38] In April 2018, Reuters reported that, "Since coming to power, Costa's government has managed to combine fiscal discipline with measures to support growth, while reversing most of the austerity policies imposed by the previous centre-right administration during the 2010–13 debt crisis.

[39] In early 2019, Costa's government survived another opposition motion of no confidence lodged over a wave of public sector strikes.

The first case appeared on 2 March 2020, and shortly after, the government declared a state of emergency, that was signed by the President, and a lockdown was also issued.

Infrastructure Minister Pedro Nuno Santos submitted his resignation in December 2022, following a public backlash over a hefty severance pay a secretary of state received from state-owned TAP, which fell under his remit.

Opposition parties said that Galamba concealed from parliament that he had proposed that then TAP CEO Christine Ourmières-Widener meet Socialist lawmakers to prepare for a parliamentary hearing about her severance package.

The laptop was later recovered by the national intelligence service SIS, leading to accusations from the opposition of a government overreach since such cases were a police matter.

[57] He added that he would reject the resignation of Galamba, keeping him in the job against president Marcelo Rebelo De Sousa's and the opposition’s request.

[58] President Rebelo de Sousa responded by issuing a warning that Costa's government needed to work on preserving its credibility, while refraining from using his power to dissolve parliament.

[59] On 7 November 2023, Portuguese prosecutors detained Costa's chief of staff Vítor Escária and named João Galamba a formal suspect[60] in an investigation into alleged corruption in lithium mining, green hydrogen production and a data centre deals.