In a normal court of law they would not have been convicted

Hold up. Let's place this person in a normal court of law with an offense of equivalent nature and scope.

Civilian A downloaded 750,000 internal documents holding proprietary and otherwise sensitive information. This was a very large organization. This civilian had special access which was granted to him in order to do his job. This civilian signed multiple NDA's, went through many months of training on how to handle this access and type of media, undertook an extremely thorough background check, and knew full well the consequences of mishandling the information. Those consequences were not only towards himself, but the organization as a whole and the people who work for it. It would also give a HUUUGGEE upper hand to their competitor(s) for years to come if had anything that he had special access to.

He noticed a pattern of misconduct that he could not tolerate on moral grounds. He reported it to his superiors, but it went nowhere. This is because all or most of the incidents had already been investigated by the right people in order to determine if changes to protocol were needed or if the laws of any kind were broken.* It may not have been a perfect system, but he did all that he could do for a person in his position.

He then decided to leak as much information as possible to and outside party who have no interest in supporting that organization, but simply want to be the source of secure information for their own purposes. Those purposes are not entirely clear, but given that party's history they will likely divulge everything to the general public.

He took steps to shield and/or obscure his identity in order to avoid punishment and maintain his position. He knew exactly what he was doing and did this over a considerable amount of time. This was not done under the influence of any substance, under threat for his life or loved ones(that we know of), and did not act on impulse. He was seen on camera stealing the data and writing it to a removable piece of media to transport it from a secure location to his own personal access. He was later caught by an undercover investigator trying to see if he would leak more of this information. That is how he was caught.

Civilian A was then charged with a crime and given a fair and speedy trial. His motives were apparent, evidence stacked against him, and the damage already done. The victim in this case was the large organization he worked for and the people who rely on people like Civilian A to not screw them over.

I don't know how to evaluate the length of sentencing, but I can say without a doubt that this was a criminal act and the evidence is admissible in a normal court of law. He would be charged for his crimes and imprisoned in pretty much any developed country.

TL,DR: If Chelsea Manning was tried in a "normal court of law," as opposed to the Court Martial administered under the Uniform Code of Military Justice, she would have gone to prison, anyway.

*Yes, I'm talking about the helicopter video.