Mahlangu has signed a three year deal with the club, the 27 year-old confirmed on his Instagram page.
According to Dinamo’s official website, Mahlangu had a medical at the National Institute of Sports Medicine in Bucharest and will join the side’s training camp in Saftica.
Mahlangu has been without a club since leaving Belgian side St Truiden at the end of last season.
The 27 year-old midfielder, who starred for Bafana Bafana at the 2013 Africa Cup of Nations, has previously also played in Sweden and Turkey.
Mahlangu has been the subject of plenty of transfer speculation linking him to Kaizer Chiefs, but the move never materialised.
Dinamo are currently second in the Romanian league after six matches, two points behind local rivals Steaua Bucharest. They are one of the most successful clubs in Romanian football history, but they have not won a league title since 2007.