Lemina, who has previously played in the Premier League for Southampton and Fulham, has agreed a two-and-a-half-year deal.
"Mario is a good player. We know him, he wants to be here, and he knows the English league," Lopetegui told Wolves' official website.
"He has the profile to help us to improve and to be able to improve our performance in the next matches.
"The transfer window is open, so we have to take advantage because we have problems in this position with few players."
Wolves are currently second-from-bottom in the Premier League and face a tricky test against West Ham this weekend, who are also struggling this season.
The club have played in two cup games over the last seven days, drawing 1-1 with Liverpool in the FA Cup before losing 4-3 on penalties against Nottingham Forest in the Carabao Cup.
The loss against Forest means Lopetegui's side missed the chance to reach the EFL Cup semi-finals, though the team will now shift their attention to performances in the league.