The Book of Mormon states that in time he proved to be a great chief captain in the Nephite army.

After fighting the Lamanite army to a standstill, Teancum and an unnamed servant enter the camp and kill Amalickiah with a javelin just before the New Year.

[7] Upon the arrival of Moroni and fellow Nephite commander Lehi, Teancum participates in a meeting to devise an appropriate plan of attack.

After Jacob the Zoramite, the commander of the Mulek occupation force, refuses an invitation to open battle, Moroni devises a "decoy and ambush" strategem.

[8] Teancum sets out to bait the Mulekites, successfully drawing them into a chase north, with Lehi waiting at the city of Bountiful.

[10] Teancum reappears as one of the co-commanders of the eastern theatre during Moroni's absence to reinstate Pahoran as chief judge.