Forest appoint Pereira as fourth boss this season
Former Wolves boss Pereira agreed an 18-month contract with Forest, who sacked Sean Dyche earlier this week.
Nuno Espirito Santo and Ange Postecoglou have also been dismissed by Forest during a turbulent campaign.
"Nottingham Forest is delighted to confirm that Vitor Pereira has been appointed as head coach on an 18-month deal," a club statement said.
Pereira will be tasked with hauling Forest away from the Premier League relegation zone.
Dyche was axed following Wednesday's 0-0 draw against bottom-of-the-table Wolves.
Pereira had been out of work since being sacked by Wolves in November after a dismal start to the season.
The 57-year-old Portuguese coach saved Wolves from relegation in 2024-25 after taking over from Gary O'Neil, but was unable to build on that success this term.
He has previously worked under volatile Forest owner Evangelos Marinakis at Greek club Olympiacos.
Pereira's first game as Forest manager will be next week's Europa League play-off round first leg at Fenerbahce.
But his main target is to preserve Forest's Premier League status.
They sit three points above the relegation zone with 12 games to go.
Forest had 35 shots on goal against Wolves but could not find a way through and Dyche was dismissed just hours after the final whistle at the City Ground.
Dyche was in charge for just 114 days following the end of Postecoglou's 39-day reign in October.
Forest's managerial mayhem comes after Nuno led them to an impressive seventh place finish in the Premier League last season.
That secured Forest's first European action since 1995-96, but disagreements with Marinakis over transfer policy led to his departure in September after 21 months in charge.
Pereira earned his reputation at Porto, where a hugely successful two-year spell saw him lead the club to back-to-back league titles.
Having spent time at Al Ahli in Saudi Arabia, he also managed Fenerbahce in Turkey and Chinese Super League Club Shanghai SIPG, as well as Brazilian clubs Corinthians and Flamengo.