Shinzon was created by the Romulans some time in the 2360's using the DNA of Captain Jean-Luc Picard. It was the Romulans' intent to eventually replace Picard with Shinzon, using him as a deep-cover operative to infiltrate Starfleet Command. However, the Romulan government was prone to frequent fluctuation and a new Praetor took power, deciding to abandon the plan. The young Shinzon was exiled to Remus where he was live out the rest of his life as a slave. During this period, he was shown pity by the Reman who would one day become his Viceroy, who taught Shinzon how to survive in the harsh environment of the Reman mines and protected him from the cruelty of the Romulan guards.
In 2374-2375, the Alpha Quadrant was thrown into war against the Dominion. During this time, Shinzon and the Remans were drafted into Romulan military service and used as expendable shock troops during many of the war's most violent battles. Shinzon survived the Dominion War, proving himself to be an excellent military tactician and combatant.
Following the end of the Dominion War, Shinzon had both military experience and a capable army at his disposal. Forming an alliance with several Romulan officials, including Senator Tal'aura and Commanders Suran and Donatra, Shinzon vowed to free his Reman "brothers". Setting into motion a plan to overthrow the Romulan government, he and his cohorts constructed a massive warbird, the Scimitar. Operating out of a secret base, Shinzon and his people also developed a weapon, utilizing deadly thalaron radiation. Deploying a small thalaron projector in the Romulan Senate, Shinzon was able to kill all the Senate members.
Shinzon's days, however, were numbered. Abandoned by his Romulan creators, Shinzon's temporal RNA aging program was never activated, and thus it began slowly breaking down his cellular structure. The only way for him to avoid death was to make a complete blood transfusion from the only genetically-compatible donor: Jean-Luc Picard.
Towards this end, Shinzon concocted an elaborate plot to lure the USS Enterprise-E (and by extension Picard) to Romulus. He planted the pieces of a Soong-type android, B-4, on Kolarus III, where he knew that the Enterprise would find it. As a result, the Enterprise was the closest starship available when Shinzon offered to open peace negotiations between the Federation and the Romulans, and Picard sailed directly into the trap.
During his first meeting with Picard and members of his crew, Shinzon remained hidden in the shadows (he and his Reman "brothers" were not comfortable in the light) and informed Picard of his intentions to negotiate peace with the Federation. After correctly guessing what Picard thought of such a negotiation, Shinzon revealed himself to his doppelgänger. This revelation shocked Picard, who now realized himself to be facing a younger version of himself. Shinzon then cut his own hand with his knife and gave the knife to Lieutenant Commander Data to have Doctor Beverly Crusher examine his blood. Afterward, he invited Picard to dinner in the Romulan Senate, insisting that they had "much to discuss".
During the dinner, Shinzon explained to Picard how and why he was created and his upbringing in the mines of Remus. Shinzon then asked with great curiosity about the history of the Picard family. Despite their obvious similarities, however, Picard was reluctant to forge a friendship with Shinzon and an alliance with his Romulan government until the Praetor had earned his trust. When Picard left, Shinzon was informed by his Viceroy that they were wasting time and reminded the young clone of their mission.
Afterward, Shinzon and the Viceroy returned to the Scimitar. Instead of proceeding with their mission, however, Shinzon had the Viceroy form a telepathic link between Shinzon's mind and that of Counselor Troi's so that he could make love with the woman he had become fascinated with. This telepathic form of rape was a violation and traumatic experience for Troi, but would ultimately assist in Shinzon's downfall.
When further delay was unacceptable because of the accelerating deterioration of his condition, Shinzon ordered B-4 to be beamed aboard the Scimitar to download the data the android had acquired from the Enterprise computer. Afterward, Shinzon kidnapped Picard by transporting him from the Enterprise's sickbay to the brig aboard the Scimitar. As soon as Shinzon left the brig, Picard managed to escape from the Scimitar with the help of Data, who had taken the place of B-4, and left the Romulan system aboard the Enterprise at maximum warp. During the subsequent trip, Data assured Picard that Shinzon would not have been him even if the two had lived the same lives, because Picard had always aspired to better himself and his understanding of the universe around him, while Shinzon sought nothing but death and destruction for those who had 'oppressed' him.
The Enterprise-E and the Scimitar engaged each other in a long drawn-out battle in a region of space called the Bassen Rift. Shinzon had intended to take Picard alive in order to harvest his blood so that it would save his own life, but after both ships were crippled, all Shinzon cared about was destroying the Enterprise and wiping out the Federation, and so he ordered the deployment of the Scimitar's thalaron projector. As the terrible weapon initialized, Captain Picard beamed aboard the Scimitar to stop it, fighting his way to the bridge where he confronted Shinzon himself. By then, Picard broke his phaser rifle after clubbing a Reman with it, so he couldn't simply shoot Shinzon as the mad Praetor advanced on him with a knife.
Picard was backed into the thalaron generator room and Shinzon closed in for the kill. To defend himself, Picard broke off an exposed pipe and as Shinzon lunged at him, he was impaled on the pipe. With his plans collapsing around him, the dying Shinzon used the last of his strength to pull himself down the makeshift spear and grab the captain by the throat. His last words to Picard were: "Our destiny is complete". As Picard stood in shock, Data arrived and transported the captain back to the Enterprise. Data then fired his phaser at the thalaron generator, destroying himself and the Scimitar and effectively concluding Shinzon's plan for galactic conquest.