The Leader of the Opposition (Portuguese: Líder da Oposição) is an unofficial, mostly conventional and honorary title traditionally held by the leader of the largest party in the Assembly of the Republic – the Portuguese parliament – not within the government; historically, since the Carnation Revolution of 1974, these have almost always been the Socialist and the Social Democratic parties.

The current Leader of the Opposition is Pedro Nuno Santos, since 2 April 2024, when Luís Montenegro took office as Prime Minister in the aftermath of the that year's snap legislative election the previous 10 March.

Due to its workings being based mostly on custom and convention, the Leader of the Opposition has a small official role, even though it is legally, honorifically, and nominally recognised.

[1] Even though the Leader of the Opposition is not entitled to a specific salary aside from the one they may have by reason of holding a public office on their own – such as that of deputy – the officeholder usually receives much more attention from the media in parliamentary sessions and activities.

It is not, however, required for a Leader of the Opposition to hold the post of deputy in the Assembly of the Republic.