Sitting 12 points clear before the start of Saturday's Championship fixtures, Wolves were waiting on the outcome at Craven Cottage after Cardiff City had moved into second earlier in the day by winning at Norwich City.
Even if Fulham had beaten Brentford at home, a win over Birmingham City on Sunday would have seen Wolves seal their place in the Championship's top two.
However, their return to the English top-flight was confirmed earlier than expected, bringing an end to a six-year absence.
It had appeared as though Wolves would have to wait until Sunday to confirm promotion after Fulham took a 70th-minute lead through Aleksandar Mitrovic.
But, in the fourth minute of stoppage-time, Brentford equalised through Neal Maupay to leave Fulham 10 points adrift of Wolves, with only three games to play.
Wolves plummeted to League One a year after their relegation from the Premier League but bounced back to the Championship after one season.
They were among the favourites to achieve promotion in 2018 having spent heavily, including signing Porto's Ruben Neves for £15.8 million.
Nuno Espirito Santo's team have been top of the table since October 2017 and could wrap up the league title if they beat Birmingham.