Jim Bennett, one of the firm's partners, represents Greitens as part of the St. Louis circuit attorney's criminal investigation of allegations that the governor threatened to release a nude photograph of a woman, taken while she was blindfolded and her hands were bound, if she spoke about their 2015 affair.
In Missouri, invasion of privacy involves capturing the image of another person without their consent.
The indictment claims that Greitens "knowingly photographed" a woman identified by her initials "in a state of full or partial nudity without the knowledge and consent" and "in a place where a person would have a reasonable expectation of privacy", according to CBS-affiliate KMOV.
The charge comes following revelations Greitens had an extramerital affair before becoming governor.
The charge stems from allegations that Greitens used a photo of his naked mistress as a form of blackmail to keep her quiet about their affair.
Kimberly Gardner, the top prosecutor in the city of St. Louis, said in a statement that the indictment involves an incident that took place on March 21, 2015.
Greitens, who was elected governor in 2016, was taken into custody and booked at the St. Louis Justice Center on Thursday afternoon.
Greitens emerged the victor in a crowded and expensive GOP primary before defeating the state's attorney general, Democrat Chris Koster, in the November 2016 election to give Republicans control of the governor's mansion for the first time in eight years.
Greitens has repeatedly denied blackmailing the woman, but has repeatedly refused to answer questions about whether he took a photo.
Greitens responded to the news on Facebook, saying he "made a personal mistake" but "did not commit a crime".
"In 40 years of public and private practice, I have never seen anything like this". With today's disappointing and misguided political decision, my confidence in our prosecutorial system is shaken, but not broken. But Elena Waskey, spokesperson for the National Governor's Association, said late Thursday that Greitens informed the organization that he would not be attending.
Greitens' attorney, in a separate statement, called the indictment "baseless and unfounded".
"I have been retained by the Greitens team, I'm one of the lawyers now", he said Monday, "and that's about all I know at this stage". My client is absolutely innocent. The House has the power to initiate impeachment proceedings against a governor.
I look forward to the legal remedies to reverse this action.
Mike Kehoe, the second-ranking Republican in the Missouri Senate, told the St. Louis Post-Dispatch that he was shocked by the news.