It is assumed Jade was the back-up plan of Shao Kahn during the second tournament, in case his own warriors would fail to withstand the fury and anger of the Earthrealm warriors. In fact, although she was not present in the first Mortal Kombat tournament, she was hiding in the shadows and watching the events unfold. From there, she would have to return to Outworld and report to Shao Kahn.
Like Kitana, Jade's origins lie not in Outworld, but in the realm of Edenia. While it is not certain whether or not her parents made any significant contributions to Edenia, it is known that they were nobles of the realm and were loyal and faithful subjects who loved King Jerrod and Queen Sindel. Aside from the fact that she has been Kitana's friend since childhood, there isn't much information on Jade's background and early life. However, it is known that Jade was kidnapped as an infant along with Kitana when Shao Khan murdered King Jerrod and took over Edenia. Jade grew up with Kitana and Mileena and was trained as one of Shao Kahn's personal assassins.
At the time of Mortal Kombat Trilogy, Kitana had been sentenced to death after pleeding guilty for treason and murdering Mileena during the events of Mortal Kombat II. She escaped the evil realm and fled to Earthrealm. Shao Kahn became enraged and appointed Jade and Reptile to venture into Earthrealm and capture her. Jade was assured that Kahn wanted her back alive, but Reptile was secretly told to bring Kitana back by any means necessary, including and especially killing her.
The two then ventured into Earth to find Kitana. However, Jade found herself torn between loyally carrying out Kahn's orders and betraying her friend or joining her against the Emperor. She ultimately decided to help Kitana and thwarted Reptile's assassination attempt. With his defeat, the path was cleared for the two women to join Raiden and his Earthrealm combatants in the battle against Shao Kahn and his forces. Of immediate importance, however, was Kitana's personal mission to reach and warn the resurrected Queen Sindel about their true past together. Jade's assistance had made that possible. With Sindel's memories recovered, she too would turn against Shao Kahn. Shortly afterward, Kahn was defeated by Liu Kang. After Kahn's defeat, Kitana would go on to free Edenia from Outworld.
Jade was not present during the events of Mortal Kombat Gold. It was at this time that Tanya betrayed Edenia to Shinnok and earned Jade's wrath.
In Mortal Kombat: Deception, it was revealed that Jade had attempted to join Kitana and her allies in the battle against the Deadly Alliance. She had arrived too late, finding her friend's body lying on the ground with the other Earthrealm warriors. Heartbroken, Jade knelt beside her fallen friend's side and noticed a large creature approaching. She then hid in the nearby shadows and witnessed this evil menace, Onaga the Dragon King, resurrect the bodies of Kitana and her fallen friends. While they were resurrected, they were also placed under an evil spell and were told to meet up with the force controlling them at the Living Forest.
Jade followed in secret, only to discover that they were going to invade Edenia and hold Queen Sindel prisoner. Jade returned to Edenia to find Queen Sindel behind bars and guarded by her own daughter. Sindel could have fought for her freedom, but she couldn't bring herself to attack Kitana. Jade attacked Kitana and managed to trap her in a cage of her own while she freed Sindel. Kitana then began shouting for the guards to capture them, forcing Jade and Sindel to flee to the portal into Outworld. Before they went through the portal, Jade caught a glimpse of her enemy, Tanya, standing next to Onaga.
Currently in Outworld with Sindel, Jade has made it her personal mission to assist her Queen in rescuing Kitana from the Dragon King's spell and to seek justice (or perhaps vengeance) against Tanya, who has betrayed Edenia yet again.
In Jade's Mortal Kombat: Armageddon ending, she is given great power by defeating Blaze. Through sheer will she opens the Pyramid of Argus. All of the darkness in the realms is drawn into it, where it is sealed forever. Jade is regarded as a hero, and the pyramid stands as a testament against anyone who wishes to do harm to Edenia.