The discount chain occupies the old BHS store with its entrance in Dudley Street and is approximately 18,000 sq ft in size.
The shop has created 55 new jobs.
Pre Purohit, store manager, said: "I think this will be great for the city centre as it will hopefully bring in a lot more trade.
"It's also been great for the community as we've created new jobs and 45 of these have gone to people who live in Wolverhampton."
Staff have worked hard for the past two and a half weeks to get the store in shape for the grand opening.
Shoppers were waiting outside b&m before it opened at 9am today ready to grab a bargain.
The store offers customers branded products at lower prices than many retailers, stocking food, clothing, gifts, home ware and household appliances.
Patricia Berry, a shopper from Cheslyn Hay, said: "It's very impressive the aisles are nice and wide so you can easily get around the shop.
"We've started to come to Wolverhampton more often now, it's good to have a shop with good prices."
New life has been brought back into the former department store after it was empty for three years.
Another shopper, Ellie Symonds from Penn, said: "I'm glad it's not just an empty building anymore as it was sad to see it going to waste after BHS closed down.
"I hope it will bring some more people into Wolverhampton and help the high street grow."
The former BHS premises has been divided into two stores and the bottom floor will be opening as a Wilko on Friday, November 15.
Wolverhampton's high street will be undergoing a number of changes in the coming months, with House of Fraser leaving the Beatties building to move into Debenhams in 2020.
Meanwhile the KFC next to Subway in Queen Square has closed but it is currently unclear whether it has permanently or temporarily shut down.