diplomatic cables in 2010 while working as an intelligence analyst in Iraq.
He also leaked video of an US helicopter attack in Baghdad in which at least nine people were killed, including a Reuters news photographer and his driver.
Prosecutors have asked for at least a 60-year prison term.
Capt Joe Morrow said in his closing argument on Monday that a long prison sentence would dissuade other soldiers from following in Manning's footsteps.
"There's value in deterrence," Morrow said.
The defence has suggested a prison term of no more than 25 years, so that Manning, 25, could rebuild his life. Defence attorney David Coombs asked for a sentence that "doesn't rob him of his youth."
Prosecutors have requested a far longer prison term than other soldiers have received in recent decades for sharing government secrets.
Army Spec Albert T Sombolay got a 34-year-sentence in 1991 for giving a Jordanian intelligence agent information on the buildup for the first Iraq war, plus other documents and samples of US Army chemical protection equipment.
Marine Sgt Clayton Lonetree, the only US Marine ever convicted of espionage, was given a 30-year sentence, later reduced to 15 years, for giving the Soviet KGB the identities of US CIA agents and the floor plans of the embassies in Moscow and Vienna in the early 1980s.
US civilian courts have ordered life in prison for spies, including Aldrich Ames, a former CIA case officer convicted in 1994 of spying for the Soviet Union and Russia and former FBI agent Robert Hanssen, convicted in 2001 of spying for Moscow.
Under military law, the verdict and sentence must be reviewed and may be reduced by the commander of the Military District of Washington, currently Maj Gen Jeffery S Buchanan.
Besides the court-martial record, Manning's defence team can submit other pieces of information in a bid for leniency.
If Buchanan approves a sentence that includes a bad-conduct discharge, a dishonourable discharge or confinement for a year or more, the case will be automatically reviewed by the Army Court of Criminal Appeals.
Further appeals can be made to the military's highest court, the US Court of Appeals for the Armed Forces, and the US Supreme Court.
Amnesty International and the Bradley Manning Support Network have announced an online petition asking President Barack Obama to pardon Manning.