WASHINGTON (This January 13 story was refiled to correct paragraph 6 to "transgender")

WASHINGTON (Reuters) - Chelsea Manning, the transgender U.S. Army soldier who served seven years in military prison for leaking classified data, is seeking the Democratic Party's nomination for the U.S. Senate seat from Maryland, according to Federal election filings seen on Saturday.

Manning, who was granted clemency by former U.S. President Barack Obama, was released in May from a U.S. military prison in Kansas where she had been serving time for passing secrets to the WikiLeaks website in the biggest breach of classified data in the history of the United States.

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Democratic Senator Ben Cardin was elected in 2006 to that seat and is expected to run for re-election this year. He is the senior Democrat on the Senate Foreign Relations Committee.

Related Coverage VIDEO Chelsea Manning eyes U.S. Senate seat for Maryland

Cardin was easily re-elected in 2012, beating his Republican challenger by 30 points in the heavily-Democratic state.

FILE PHOTO - Chelsea Manning, the transgender U.S. Army soldier responsible for a massive leak of classified material, poses in a photo of herself for the first time since she was released from prison and post to social media on May 18, 2017. Chelsea Manning/CC BY-SA/Handout via Reuters

Manning had been working as an intelligence analyst in Iraq. She was convicted by court-martial in 2013 of espionage and other offenses for furnishing more than 700,000 documents, videos and diplomatic cables to WikiLeaks, an international organization that publishes information from anonymous sources.

She came out as transgender shortly after her sentencing, but the military denied her request for hormone therapy treatment while behind bars. She was placed in solitary confinement after attempting suicide twice.