The robbed banker had been tasked with delivering the cash, a mix of dollars and euros, to another branch of his bank, said a court official in Manouba, where the robbery happened.
The banker, accompanied by a driver and the security guard, received a call from his plumber. So, the banker requested that they make a detour to his home, where he got out of the vehicle - leaving the bag.
When he returned, he found that the guard had given the driver the slip and fled with the cash, Sondos Nouioui, Manouba court spokeswoman, told Tunisian media.
Nouioui said the suspect, who had worked for four months for a private security firm, was a notorious criminal and the subject of no fewer than 10 wanted notices.
His whereabouts are not known but he is believed to be flush with cash.
Both the driver and the banker were detained by authorities.