He tweeted a photo of himself from the account Monday morning, showing the former lawman sporting sunglasses and standing in the middle of an Iowa road. "Will try to tweet in useful ways", a comment sure to be interpreted as a jab at his prolifically tweeting former boss.
Comey has a book due out next spring.
Comey tweeted a picture from Iowa revealing his secret Twitter account. President Donald Trump fired Comey dramatically in May, and Comey has since remained out of the public spotlight with the exception of an appearance before a congressional committee about his ouster.
Comey has maintained a relatively low public profile since being dismissed as Federal Bureau of Investigation chief, a move which came amid an Federal Bureau of Investigation probe into whether any members of Trump's 2016 White House campaign colluded with Russian Federation. The firing ultimately led to the appointment of a special counsel, which has dogged the Trump presidency for months.
The account operates under the name Reinhold Niebuhr - a theologian and political commentator who died in 1971 - and has been the subject of investigations from Gizmodo and the New Yorker, among other outlets.
Another shows birds in flight with the notation "Watching migrating white pelicans in Iowa thinking about Niebuhr's Serenity Prayer". Monday's post appeared to confirm the theory.
Iran tension and doubts over Iraq supplies stabilise oil prices
The American Petroleum Institute (API), an industry trade group, will release USA weekly petroleum inventory data at 4:30 p.m. Oil prices rose after Iraqi forces entered Kirkuk, briefly cutting some crude output from OPEC's second-biggest producer.
Comey is married to Patrice Failor, who is an Iowa native.
Unlike Trump, whose preferred form of communication is Twitter, Comey has not been prolific on the social media site.
'Actually I'm not even mad.
The meme was accompanied by a link to the FBI's hiring page, fueling further speculation.
Being outed drew more than 8,000 followers to the account within an hour.