The election, the third in as many years, was called just one year into the minority government's term after Prime Minister Luis Montenegro failed to win a parliamentary vote of confidence in March when the opposition questioned his integrity over dealings of his family's consultancy firm.
Montenegro has denied any wrongdoing and most opinion polls showed that voters have dismissed the opposition's criticism.
The election, also dominated by issues such as housing and immigration, follows a decade of fragile governments; the only one of which to have a parliamentary majority still collapsed halfway through its term last year.
Exit polls published on Sunday by the three main television channels - SIC, RTP and TVI - put Montenegro's AD as receiving between 29 per cent and 35.1 per cent of the vote, garnering the biggest share but again no parliamentary majority, similar to what happened in the previous election in March 2024.
According to the exit polls, Montenegro's main rival, the centre-left Socialist Party (PS) garnered between 19.4 per cent and 26 per cent of the vote, nearly tied with the far-right Chega party's 19.5-25.5 per cent share, which is higher than the 18 per cent it won in 2024. Montenegro has refused to make any deals with Chega.
Political scientist Antonio Costa Pinto said the new parliament would likely be similar to the last, and it was impossible to predict how long the government would last, as it depended on factors ranging from the international situation to the AD's ability to reach deals with other parties.
"The only doubt is whether the AD will form a new minority government ... or whether it will form a post-electoral coalition with IL, even if this coalition does not guarantee an absolute majority," he said, referring to the pro-business Liberal Initiative (IL) party.
IL, a party some analysts see as a potential coalition ally of the AD, was likely to garner four to eight per cent of the vote, meaning its potential alliance could only reach a majority of 116 in the 230-seat parliament if both perform at the top of the exit poll estimates.
Portugal has outperformed most European Union countries on economic growth, and run budget surpluses and reduced its debts under both centre-left and centre-right governments.
But further political instability could delay major projects such as lithium mining in the north, and potentially compromise the long-delayed privatisation of the TAP airline.
