Before the onset of the Mandalorian Wars, Master Vandar taught many pupils, including Zayne Carrick and the Jedi Exile. At one point, Vandar discussed the abilities of the Exile with Master Vrook Lamar. Master Vandar saw the immense potential of the Exile and believed him to be a natural leader who would remain a Jedi, while Master Vrook saw the Exile as weak in the Force and believed he would eventually fall to the dark side.
By 3,964 BBY, Vandar was the head Master of the Dantooine Jedi Enclave. Having faith in fellow Jedi Masters, he refused to believe Zayne Carrick's allegations when the fugitive Padawan told him about the Padawan Massacres of Taris. Instead, he suggested that Zayne himself may have committed the crime and not recalled it correctly.
Vandar was believed to have seen a vision of a horrible war, in which the galaxy would be placed in darkness, as revealed by Bastila Shan on Taris. It is not known what exactly he saw, but it was this vision that caused the Jedi Council to not act in the Mandalorian Wars.
It is also believed, at least by some, that the true vision Vandar saw was that of the True Sith returning to Republic space. However, this is just speculation.
He was presumed killed by Darth Nihilus, as the Sith Lord used his powers to destroy all life on the planet of Katarr during the Jedi Conclave there. However, there was a small chance that the Jedi Master stayed away in hiding like Masters Kavar, Vrook and Zez-Kai Ell after realizing that the Jedi Order was too weak and scattered to fight this new Sith threat.