The former mayor of Lisbon took the reins in 2015 following a ballot in which his Socialists finished second behind a centre-right coalition that had overseen a harsh EU-imposed austerity program.

In a surprise move, he convinced two smaller hard-left parties to support a minority Socialist government, the first time this had been tried in Portugal.

Many analysts predicted the coalition government -- dubbed the "geringonca" or "contraption" -- would last six months at most, but it completed its four-year mandate.

Costa then led his Socialists to victory in the next election in 2019, although they fell short of an outright majority.

On Sunday, he finally scored an absolute majority in parliament in a snap election that saw his Socialists win at least 117 seats in the 230-seat parliament, according to results.

Four seats still need to be attributed in the coming days with the results of votes cast abroad, but in 2019 the Socialists obtained two.

"I have to admit that tonight is very special to me," Costa said during a victory speech at his party's campaign headquarters.

'Annoying optimism'

Riding the wave of the global economic recovery and a tourism boom, Costa, 60, managed to undo some of the austerity measures imposed by his predecessors even as his government balanced the books.

On his watch, Portugal in 2019 posted its first budget surplus in 45 years of democracy although the Covid pandemic has since caused the public deficit to balloon once again.

But in October 2021, Costa failed to secure budgetary support from the two smaller far-left parties propping up his government, prompting Sunday's snap polls.

Before Sunday's election he had vowed to step down if his Socialists did not win but he also signalled his willingness to once again form alliances if it came out on top without a majority.

"Antonio Costa is a very experienced and very ambitious politician," said University of Lisbon political scientist Jose Santana Pereira.

"In some contexts there are characteristics that are good qualities, in others they can be seen as flaws."

But Portugal's conservative President Marcelo Rebelo de Sousa, who was Costa's professor at law school in Lisbon, once called the premier out for his "chronic and slightly annoying optimism".

Family from Goa

Born in Lisbon on July 17, 1961, Costa was raised in the intellectual circles frequented by his parents, Orlando da Costa, a communist writer descended from a family from Goa, Portugal's former colony in India, and Maria Antonia Palla, a journalist and women's rights advocate.

Nicknamed "babush", a term of endearment for a little boy in Konkani, a Goan dialect, Costa joined the youth wing of the Socialist Party in 1975 when he was just 14, a year after a coup ended a decades-long right-wing dictatorship.

in 1995, after earning a law and political science degree, Costa was named secretary of state for parliamentary affairs -- a key role in the Socialist minority government of Antonio Guterres, the current UN secretary-general. 

Costa was promoted to justice minister four years later.

Following a brief stint as a member of the European Parliament, he was appointed interior minister in 2005 in the government of Jose Socrates.

He stepped down after two years and made a successful run for mayor of Lisbon. He was re-elected to the post in 2009 and 2013.

The move to municipal politics allowed Costa to distance himself from Socrates, who stepped down as premier in 2011 after negotiating Portugal's international bailout. 

Socrates was arrested in 2014, accused of corruption and tax evasion.

A fan of Lisbon-based Benfica, Portugal's most successful football team, the married father-of-two likes to relax by doing jigsaw puzzles.

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