Though she has yet to comment on the filing, the Washington Post reports that the candidate is the same Manning who, while working as an intelligence analyst in the United States army, leaked a trove of classified documents to WikiLeaks, was sentenced to 35 years in prison for doing so, and had her sentence commuted by president Barack Obama after serving seven years. She will run as a Democrat.
She is running as a Democrat and will likely challenge two-term Sen. With 21 convictions in total, she was sentenced to 35 years at a maximum security prison at Fort Leavenworth.
Former president Barack Obama granted her clemency before leaving office previous year.
Manning could not immediately be reached for comment.
In 2010, Manning was arrested after she provided a trove of almost 750,000 documents to Wikileaks that included documents about the war efforts in Iraq and Afghanistan, State Department cables, and information about prisoners in Guantanamo Bay.
Reports said Ms Manning moved to Maryland after her release and friends and family raised more than $175,000 to support her through an online campaign. In September, a profile of Manning in Vogue magazine ran alongside a picture of her in a swimsuit, taken by famed photographer Annie Leibovitz. Nevertheless, many others label her a traitor for leaking sensitive data on the wars in Iraq and Afghanistan, as well as the inmates in Guantánamo.
"I've had people telling me, 'Maybe you shouldn't be so vocal.' And that's the reason why I'm out here", she said, explaining that she "can't imagine doing anything else right now". The state's senior senator is an overwhelming favourite to win. Ben Cardin in this year's election.
Manning, a 30-year-old transgender woman born as Bradley, has been a controversial figure in the social networks ever since being released from a Kansas prison in May 2017.