The 21-year-old moved to Bristol City on loan at the start of the season until Christmas but he tore his hamstring within minutes of coming off the bench and returned to Molineux.
Vokes made two substitute appearances for Wolves in the FA Cup this season against Doncaster and Stoke after recovering from the injury.
He joined up with the Bramall Lane club, who are three points from safety in the third relegation spot ahead, of their clash with Reading.
His signing follows that of Fulham midfielder Bjorn Helge Riise earlier in the day.
Source: PA
Source: PA