As reported by Goal on Thursday, the deal contains an option for Spurs to sign him outright for £41 million ($53m) at the end of the season.
Spurs will pay an initial loan fee of €3m, which would be deducted from the final price if Jose Mourinho decides to make his move permanent.
Vinicius was the joint-top goalscorer in the Primeira Liga in 2019-20, scoring 24 goals in 47 games in all competitions.
Mourinho will be hoping Vinicius can provide competition and a much-needed rotation option for Harry Kane. Previous backups such as Fernando Llorente and Vincent Janssen have generally failed to deliver on a consistent basis.
Kane's fitness has caused something of a scrap between Mourinho and England manager Gareth Southgate of late, though he has started the season in good form with six goals and six assists in seven appearances.
Spurs fans may be hoping Vinicius can follow in the footsteps of Raul Jimenez, who has shone in the Premier League since joining Wolves from Benfica in 2018.
He follows Gareth Bale, Sergio Reguilon, Matt Doherty, Pierre-Emile Hojbjerg and Joe Hart to north London as Mourinho reshapes his squad.
Spurs had been hopeful of finding a deal with Juventus to sign defender Merih Demiral once Vinicius arrived, but Goal understands Juve will not allow the Turkish international to leave.
Inter defender Milan Skriniar is also of interest, though sporting director Piero Ausilio says he is not available either.
Tottenham's next fixture will be a meaningful one for Mourinho, as he returns to his former home of Old Trafford on Sunday to face Manchester United in the final game before the international break.