Bradley Manning, the US soldier convicted of the biggest breach of classified data in that country's history, will be told how much of his life will be spent in a military prison.
The judge hearing Manning's court-martial, Colonel Denise Lind, is due to read his sentence at 10:00 am local time (14:00 GMT) on Wednesday.
Manning faces up to 90 years in prison for leaking more than 700,000 Iraq and Afghanistan battlefield reports and US State Department diplomatic cables in 2010 while working as an intelligence analyst in Iraq.
He also leaked video of a US helicopter attack in Baghdad in which at least nine people were killed, including a Reuters news photographer.
Prosecutors have asked for the judge to apply at least a 60-year prison term.
Manning's defense argued that his aim had been to "spark a broader debate" on the role of the US military and make Americans aware of the nature of wars in Iraq and Afghanistan.
According to defense testimony, military supervisors ignored erratic behavior on the part of Manning which included trying to grab a gun during a counseling session.
Last week, Manning apologised to the court for what he had done, saying "I understand I must pay a price for my decisions."
Manning's attorney David Coombs will also ask for a pardon from US President Barack Obama, The Bradley Manning Support Network, a group backing the soldier said.
In July, Manning was found guilty of 20 criminal counts including espionage and theft, but not of aiding the enemy, the most serious charge, which carried a possible sentence of life in prison without parole.