In 2010, former Army private Chelsea Manning was arrested after she provided almost 750,000 documents to WikiLeaks that included information about prisoners in Guantanamo Bay and USA war efforts in Iraq and Afghanistan.
Manning's filing was received January 11, according to Federal Election Commission records.
Cardin was easily re-elected in 2012, beating his Republican challenger by 30 points in the heavily-Democratic state.
When another Twitter user criticized Manning's diatribe on police last week and said "have fun never voting again", she responded that she was registered to vote despite her criminal record: "state of maryland doesnt disenfranchise".
In 2013, Manning was convicted for 35 years for the largest leak of classified documents in USA history, which included military information about the war in Iraq and Afghanistan and State Department cables. The primary is set for June 28.
Now, she is throwing her hat in the ring against a member of the Democratic establishment, Senator Ben Cardin, who also hasn't commented on the putative challenge. "The world is a better place with her as a free woman, and this latest news makes it clear she is only beginning to make her mark on it".
Known as Bradley Manning at the time of her 2010 arrest, Manning came out as transgender after being sentenced.
Three years later, Manning was convicted of multiple counts, including violating the Espionage Act, and received a lengthy sentence.
The case and Manning herself continue to be politically divisive in the United States. 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.
During her incarceration Manning battled for, and won, the right to start hormone treatment.