"This great war must be stopped before it starts...or millions of lives will be lost."
- – Lenonn to Delenn
Lenonn served in the Rangers for decades eventually rising to lead the organization. Over the years, the Rangers had been seen as little more then an embarrasment. In fact, their funding and personnel had been greatly reduced. In 2243, Lenonn requested more support for the Anla'Shok from the Warrior Caste. This request was denied. The Warrior Caste's messenger, Callier, made it clear that the caste-elders felt that the Rangers were an unnecessary burden. Further, he told Lenonn that if he forced the issue by going to the Grey Council directly he might lose the little support he had left. Believing in the prophecies of Valen, Lennon felt that the time had come when the Rangers were the most needed, so he requested to take his case before the Grey Council. A group from the council came in the middle of night and collected him.
After Lenonn's audience with the Grey Council, it was decided that the council would visit Z'ha'dum to see if the Shadows had begun moving, as prophesied. This expedition would lead to the disastrous first contact between the Minbari and the Humans, sparking the Earth-Minbari War. 
Lenonn would also develop a friendship with Delenn after these events. Lenonn recreated the sanctuary of Dukhat aboard the Grey Council's ship, including bringing two Vorlons aboard; allowing only himself and Delenn access.
The two agreed that the war was out of control and that it needed to end. They agreed that Lenonn himself would meet a delegation of humans and open negotiations. It was agreed that the other Minbari leaders would respect Lennon's decision and abide by it. To this end, Lenonn would later have his Rangers initiate contact with the Narn Regime to arrange a secret meeting with Earth Alliance representatives to discuss a peaceful end to the war. The meeting took place in the Epsilon System, though was cut short when the site was attacked from orbit. Lenonn died from his injuries before the other Minbari came looking for him, resulting in an escalation in the conflict.