He is currently writing a book due in the spring and which critics of Trump hope will include more revelations about his relationship with the president. Now they have an extra source to monitor for damaging nuggets.
It will also spark speculation that he is preparing a 2020 White House run. Iowa is one of the early voting states in the nomination race that can make or break a campaign.
Comey's tweet confirms an investigation in March by Gizmodo that concluded he was the "Reinhold Niebuhr" behind the mysterious @formerbu account.
The real Reinhold Niebuhr was an America theologian and public intellectual who died in 1971 - and who served as the subject of a student thesis written by Comey in 1982.
His teachings are heavily in vogue among American politicians on both the Left and the Right. Barack Obama is among those who have described their admiration for a philosopher who tried to reconcile humankind's flawed nature with its ongoing quest for justice.
The little used Twitter account posted photographs of West Point and Gettysburg in recent months, and more recently featured bucolic scenes from around Iowa.
Benjamin Wittes, editor in chief of the Lawfare blog and a friend of Comey's, confirmed that account belonged to the former FBI chief.
