The defender-come-midfielder parted ways with Celtic after asking the club to terminate his contract just two months into the current season.
Ndengane has since been included in the Bucs squad ahead of their upcoming Caf Champions League campaign.
A club statement reads: "After a hiatus of three years, Orlando Pirates make a welcome return to continental football in the form of the CAF Champions League next month."
"The Mighty Buccaneers will be welcoming Light Stars to Orlando Stadium for the midweek fixture of 27-28 November, before taking a trip to Seychelles for the return leg on 4-5 December."
"Success over these two legs will see the Buccaneers go on to the second round where they will face the winner of the match between Volcan de Moroni of Comoros or Namibia’s African Stars."
"Meanwhile, the club has registered a 27-man squad ahead of these two crucial rounds."
Ndengane, who has been training with Bucs since last month, cannot be used by the Soweto giants until they register him with the PSL in January 2019.
However, the former FC Cape Town player can only play in the Caf Champions League for now.
Pirates' Caf Champions League squad:
Goalkeepers: Siyabonga Mpontshane, Jackson Mabokgwane, Brilliant Khuzwayo.
Defenders: Happy Jele, Ntsikelelo Nyauza, Marshall Munetsi, Alfred Ndengane, Mthokozisi Dube, Abbubaker Mobara, Abel Mabaso, Asavela Mbekile, Innocent Maela, Paseka Mako, Caio Marcelo.
Midfielders: Musa Nyatama, Xola Mlambo, Ben Motshwari, Mpho Makola, Linda Mntambo, Meshack Maphangule.
Forwards: Thembinkosi Lorch, Augustine Mulenga, Thabo Qalinge, Vincent Pule, Justin Shonga, Thamsanqa Gabuza, Kudakwashe Mahachi.