The young striker joins the Team of Choice as part of the deal which saw Lebohang Maboe move to the Brazilians last week.
Media reports emerged less than a week ago that Makgalwa would join Maritzburg United, but the club remained silent, probably because the deal had not been concluded.
Maritzburg United took to their social media to unveil Makgalwa although the extent of the player's contract was not disclosed.
KELETSO MAKGALWA 🔵⚪️
Maritzburg United are pleased to announce the signing of Keletso Makgalwa on a season-long loan deal.
The 21-year-old joins the Team of Choice as part of the deal which saw Lebohang Maboe sign for the Brazilians.#WeAreUnited pic.twitter.com/3xcHtQJXoO — Maritzburg United FC (@MaritzburgUtd) August 7, 2018
Makgalwa was promoted to the Sundowns first team last year, but he struggled to feature regularly under Pitso Mosimane.
The 21-year-old made a mere four appearances for the Tshwane giants without finding the back of the net.
He will be hoping to leave his mark at the KwaZulu Natal-based this season, especially with Fadlu Davids known for his affection to work with young players.
Makgalwa was seen as a possible replacement for Percy Tau, who left Sundowns
Makgalwa follows his former MDC teammate Thendo Mukumela, who joined Ajax Cape Town on a permanent deal on Tuesday morning.