Manning faces up to 90 years in prison for giving the anti-secrecy group WikiLeaks more than 700,000 US military and diplomatic documents and battlefield video documenting civilian deaths.
The judge, Colonel Denise Lind, said she could announce the sentence as early as today.
The prosecution has said Manning should spend 60 years in prison because he betrayed the US. The soldier's lawyer did not recommend a specific punishment but suggested any prison term should not exceed 25 years, saying the classification of some of the leaked documents expires in 25 years.
Defence lawyer David Coombs said Manning, who was 21 when he enlisted, had limited experience in life and in the military. His youthful idealism contributed to his belief he could change the way the world viewed the wars in Iraq and Afghanistan, and all future wars, by leaking the secret files.
Prosecutors have called Manning an anarchist computer hacker and attention-seeking traitor. The soldier's supporters have hailed him as a whistleblower.
Prosecutors did not say why they were not seeking the maximum punishment for Manning, who was convicted last month of 20 offences, including six violations of the Espionage Act and five counts of stealing protected information.
The prosecutors' request for 60 years probably reflects their view Manning's offences were less severe than if he had specifically sought out foreign agents.