The younger brother of Orlando Pirates and Bafana Bafana player Siyabonga has agreed to join the Brazilians for the 2012-13 season
Sangweni, who was also linked to Orlando Pirates, has signed a three year contract after passing his medical test on Tuesday.
Usuthu publicist Philani Mabaso confirms that the midfielder has been cleared to play for the Brazilians.
"I can confirm that Thamsanqa Sangweni is now a Mamelodi Sundowns player after he agreed on personal terms with the club on Tuesday," said Mabaso, according to Kickoff.com.
"We wish him all the best in his soccer career with Sundowns," he added.
Meanwhile Mabaso also confirmed that his club has cleared goalkeeper Nhlanhla Khuzwayo to join Kaizer Chiefs.
Usuthu have also terminated the contract of striker Stanton Lewis after only spending one season with the club.