"H&M has great faith in the concepts, which are judged to have great potential for the future," the company said in a statement on Wednesday.
FaBric Scandinavien will be incorporated fully into the H&M Group, but the brands will continue to be operated as separate concepts, the company added.
In the spring of 2008, H&M acquired 60 percent of the shares of privately owned FaBric Scandinavien AB through a cash purchase.
The purchase agreement also included an option to acquire the remaining shares in FaBric Scandinavien. H&M has now exercised this option and purchased the remainder of the shares.
The purchase price for the other 40 percent of the company was 8 million kronor ($1.15 million) in cash, making the total price paid by H&M for FaBric Scandinavien 552 million kronor.
The company has expanded substantially since the acquisition two years ago, more than tripling the number of stores in the network to 66 from 20. Weekday and Monki stores now operate in seven countries.
"The expansion and international roll-out of Weekday, Monki and Cheap Monday will continue," the company said.
The company was sold by its founders Adam Friberg, Lars Karlsson, Örjan Andersson and Linda Friberg.