US military judge Denise Lind plans to issue her judgment at 1700 GMT, as the trial, which got under way in June, draws to a close.
Lind will decide whether Manning was a traitor who committed espionage against his country and aided America's enemies, or a whistleblower who hoped to shine a spotlight on what he felt was US government misconduct.
Manning was serving as an intelligence analyst in Iraq when he sent WikiLeaks a vast cache of secret diplomatic cables and classified military reports from the wars in Iraq and Afghanistan.
The 25-year-old has admitted giving the anti-secrecy website some 700,000 documents, pleading guilty to 10 lesser charges, including espionage and computer fraud, which could carry a prison sentence of up to 20 years.
But Manning has denied other charges, including the most serious one - that he knowingly helped enemies of the United States, most notably Osama bin Laden and al Qaeda.
If convicted of "aiding the enemy," he could spend the rest of his life in jail. But even without it, the other charges could add up to 154 years imprisonment. The sentencing phase of the trial could begin as early as Wednesday.
To find Manning guilty of "aiding the enemy," the judge must be convinced beyond reasonable doubt that the soldier knew the documents he leaked could end up in the hands of al Qaeda.
In closing arguments, defense attorney David Coombs said Manning was no traitor but a "young, naive and good-intentioned" citizen who wanted to encourage public debate about US foreign policy.
Most of the information he sent to WikiLeaks was published between April and November 2010.
In a preliminary hearing in February this year, Manning read a long letter justifying his actions, in which he spoke of the "bloodlust" exhibited by a US Apache helicopter crew who gunned down a group of Iraqis in Baghdad.
But the prosecution insists Manning recklessly betrayed his uniform and his country by leaking documents he knew al Qaeda would see and use.
"He was not a troubled young soul, he was a determined soldier with the knowledge, ability and desire to harm the United States in its war effort," lead prosecutor Major Ashden Fein told the court.
"Your honor, he was not a whistleblower, he was a traitor."
Manning's supporters argue a conviction would be a huge blow for press freedoms in the United States and would deter future whistleblowers from exposing government wrongdoing.
His attorneys have argued that Manning was disillusioned by the horrors of war, and leaked the documents out of a desire to alert the US public that it was being misled by its government.
In a statement Monday, the Bradley Manning Support Network called it an "ominous sign" when Judge Lind, they claimed, "altered important charges last week in order to assist prosecutors ahead of her verdict."
According to the group, which cited defense lawyers, three of five theft charges were modified in their wording, now including language that refers to information theft.
Without being allowed to return witnesses to the stand, at this stage of the trial, to question them on the newly worded charges, the defense lawyers are asking the judge to dismiss them.
Under the rules of a court martial, they said in a statement, "a military judge may declare a mistrial when 'manifestly necessary in the interest of justice because of circumstances arising during the proceedings which cast substantial doubt upon the fairness of the proceedings.'"
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ