The 31-year-old Bafana Bafana winger had been without a club since leaving Qatar Stars League outfit Qatar SC at the end of last season.
He joins the Asian outfit, where he will play alongside a familiar face in ex-Kaizer Chiefs midfielder Njabulo Blom, who signed signed with the club last month.
Tau initially joined the Qatari side from Al Ahly in January on a short-term six-month contract with an option to extend, but the two parties parted ways after just one campaign.
During his stint in Qatar, Tau made 10 appearances, registering four assists and playing a key role in helping the club avoid relegation. They ultimately finished 10th in the 12-team championship, just two points clear of the drop zone.
Despite reported interest from Egypt's Zamalek SC, a Moroccan Botola Pro League side, and even rumours linking him with Kaizer Chiefs, no deal materialised until Nam Dinh came calling.
The Witbank-born attacker has now signed a one-year deal with the Vietnamese giants, with an option for a further 12 months.
Tau and Blom will add much-needed experience to a squad preparing for continental competition. Nam Dinh, who clinched the V.League title last season with an eight-point cushion over rivals Hanoi, have secured qualification for the Asian Champions League.
For Tau, the move marks a new chapter in a career and he will look to make his mark in Southeast Asia while helping Nam Dinh chase success at both domestic and continental level.