Following his father's death commanding the ChR Gal Gath'thong, Jannek served the Romulan Star Empire, and eventually became an ambassador. His interests in adulthood included hunting, and history, with a particular personal interest in Federation history and exploits of James T. Kirk.
At some point in his career, Jannek established a friendly relationship with Federation Ambassador Curzon Dax.
Circa 2371, Jannek gained access to his father's final logs, which had survived the destruction of his vessel, and was inspired by Keras's final words to Kirk: "In a different reality, I could have called you friend." Also around that time, he traced the Kirk family tree to the present, and discovered the existence of Jamie Samantha Kirk, who had recently graduated from Starfleet Academy, and developed an interest in the young Human.
Around that time, Jannek was sent as an envoy to Bajor to try and establish a relationship between the Romulan Star Empire and the Bajoran people. He and a small force of Romulan military personnel under his command stayed on Deep Space 9 for duration of the talks.
As Jannek arrived on the station, an apparent malfunction in the docking ring caused the death of a Starfleet lieutenant. Jannek and his party accompanied the medical personnel to the infirmary, where he met, and reacquainted himself, with Dax, now in its new host Jadzia, and to his surprise Jamie Samantha Kirk, who had recently been assigned to the station.
Following the accident, Jannek had his men scout around the station to seek an unusual activity. One of his men, Lieutenant Rykhin, became aware of an artifact Kirk, Dax, and Doctor Bashir had recently brought back from the Gamma Quadrant, and later became aware of a plot to steal it. When the Rykhin attempted to stop the plot, he was shot and killed by the thief. The thief disappeared in an energy-surge from the artifact.
Realizing the artifact might be dangerous Kirk, Dax and Bashir opted to continue studying it on the USS Orinoco away from the station. Unfortunately shortly after they launched the runabout was hijacked by stowaways, members of Bajoran isolationist group, the Circle, who believed the artifact was the Chalice, and that it would allow The Circle rise to power on Bajor.
Jannek persuaded Commander Sisko to let him join a rescue party. By tracking a homing signal Dax had been able to activate aboard the Orinoco, Jannek and the team from DS9 took the USS Rio Grande in pursuit, and found The Circle personnel performing a ritual on Bajor to celebrate their acquisition.
However, the artifact was not the Chalice, and an energy buildup knocked The Circle's leader out as the artifact grew and revealed its true purpose – the artifact was in fact Ayelborne, the last of the Organians, nearing the end of his journey to another plane of existence. Before he departed, he wished to bring peace between the Federation and Romulans, much as he and the other Organians had begun a century earlier between the Federation and the Klingons, and as such had engineered the recent events to bring Jannek and Kirk together. It was hoped by Ayelborne that the pairing could form the start of a peaceful relationship between the interstellar powers.
Inspired by Ayelborne and his late father's hopes of peace, Jannek requested that Ensign Kirk serve as his liaison officer with the Federation, and offer she willingly accepted. (DS9 comic: "Blood and Honor")
- Alien Spotlight: Romulans established Keras' family before he left on the mission depicted in "Balance of Terror". The sequel to that comic, Romulans: The Hollow Crown, followed the family after the episode and named them, identifying Keras' son as Gaius, and his wife (Gaius' mother) as Arenn. While it is possible Jannek was a second son in that family, in the story the Praetor orders them put to death, and only Arenn and Gaius are present. It is entirely possible that Keras's son either had multiple names at birth, or else went by the name Jannek at some point in the future, when he got older.
- In Blood and Honor, after Kirk accepted Jannek's offer he says, "[An] old family friend awaiting you is glad you joined our cause," presumably indicating Jannek was in some way affiliated with Spock and the reunification movement.