Sarkozy, who led the country between 2007 and 2012, is accused of illegally financing his failed re-election campaign, Herzog confirmed.
The 62-year-old, who was beaten by Francois Hollande five years ago, is set to appeal against the trial order, according to Reuters.
Reuters says Herzog described the order as "inane" and said that only one of the two magistrates in charge of the case actually signed the order.
"The clear disagreement between the two magistrates in charge of the matter is such a rare event that it is worth underlining, as it illustrates the inanity of the decision," he said in a statement, according to Reuters.
The news comes at a time when the French presidential race has become embroiled in allegations of financial wrongdoing.
On Monday, Republican nominee Francois Fillon, who defeated Sarkozy in November's primary, said he would fight on
despite his campaign having been dogged by corruption allegations.
The investigative newspaper Le Canard Enchainé published new allegations that Fillon's wife, Penelope, and two of his adult children were paid hundreds of thousands of euros for work they did not do.
In his speech, Fillon stated that he had "nothing to hide" and that his wife Penelope's salary of over 3,500 euros a month was "perfectly justified."
He insisted that Penelope worked for 15 years as his "deputy," carrying out several roles, including managing his schedule and representing him at cultural events.
Fillon also said that his daughter and son were also employed in similar positions for 15 months and six months respectively.
While adding that employing his family was not illegal, Fillon did acknowledge that it was an "error of judgment" and offered an apology to the French people.
This is not the first time Sarkozy has come under scrutiny by authorities in France.
In 2014 he was investigated by prosecutors after allegations surfaced that he sought to influence judges, who were examining claims that the former president received secret financing during his successful 2007 election.
Sarkozy was accused of plotting to obtain confidential information about the investigation in exchange for giving a high-ranking magistrate a prestigious post.
The case hinged on secret telephone recordings between Sarkozy and his lawyer Herzog but it wound up last year without either man being charged.
Sarkozy was also cleared of allegations that he received money from L'Oreal heiress Liliane Bettencourt to finance his 2007 election campaign.
Sarkozy is far from alone when it comes to French politicians brushing with the law.
Former President Jacques Chirac was convicted in 2011
of misusing public funds to ensure his political allies remained in non-existent jobs. He received a two-year suspended sentence.
In early February, Marine Le Pen, the far-right candidate for the upcoming election, missed a deadline
for repaying 300,000 euros that the European Parliament says she misused.
Le Pen denied the allegations in an interview with CNN and characterized the issue as a "political attack." She said she would refuse to pay back the money.