The Pentagon said Monday that Maj. Gen. Jeffrey Buchanan approved the 35-year sentence, rejecting a request for clemency. Manning, who now goes by the name Chelsea and has said she is female, is being held at the U.S. Military Disciplinary Barracks at Fort Leavenworth.
Manning was convicted by a military judge of leaking 250,000 diplomatic cables and 500,000 military documents to WikiLeaks while serving in Iraq. Published material from his leaks is credited with helping kickstart the Arab Spring demonstrations since it included U.S. cables giving an unflattering picture of former Tunisian President Zine El Abidine Ben Ali.
Col. Denise Lind acquitted Manning of aiding the enemy but found him guilty of most other charges and sentenced him to 35 years.
Nancy Hollander, Manning's lawyer, said she had not expected much from the automatic military appeal process. She said she plans to continue appeals.
President Obama has said he will not make any decision on executive clemency until Manning's appeals are exhausted, a process that could outlast his presidency.
Manning is seeking court approval of the name change in Kansas.