Ben Cardin in the June Democratic primary.
Manning declared in Federal Election Commission filings, dated January 5, her statement of candidacy to run as a Democrat in the 2018 election.
The race would pit her against two-term Sen.
The 30-year-old Manning listed a North Bethesda address in her FEC filing.
Chelsea Manning is running for Maryland's Senate
Manning, then known as Bradley Manning, was arrested in 2010 and convicted in 2013 of leaking a trove of sensitive documents to WikiLeaks. She is running as a Democrat.
She came out as transgendered shortly after her sentencing, but the military denied her request for hormone therapy treatment while behind bars.
The information Manning disclosed included low-level battlefield reports from Iraq and Afghanistan, Guantanamo prison camp detainee profiles and US diplomatic correspondence.
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.
President Barack Obama commuted Manning's sentence in January 2017 and Manning was released from prison in May 2017.More news: Khan fight no issue for Spence