Usni was the son of Mom Rajawongse Seni Pramoj, twice Prime Minister and one of the major political figures of 20th-century Thai history, and Khunying Usana Pramoj Na Ayutthaya.

[1] In his youth he attended Bangkok Christian College before studying law at the University of Oxford.

[2] A lawyer by profession, Usni began his career as a judge advocate in the Ministry of Defence.

He was an honorary[verification needed] Admiral of the Royal Thai Navy.

Usni was a distinguished a violinist and composer who founded the Bangkok Symphony Orchestra and was twice named a National Artist of Thailand.