Both men were on patrol duty along the border belt when the incident happened Monday night near village Chhina Bidhi Chand, 50 km from Amritsar.
Tarn Taran district police chief Kamaljit Singh said Sunil Kumar, 28, of the Border Security Force shot dead Mahesh Kumar, 27, before committing suicide. Mahesh died on the spot.
BSF personnel told police that Sunil Kumar suddenly became enraged over something.
Punjab has a 553-km barbed wire border with Pakistan, manned round-the-clock by the BSF.
