Sambuu was born in 1895 in what is now Büren sum of Töv Province. The son of a shepherd and cattle farmer, he became a clerk in local and provincial administrations at age 16. Following the Mongolian Revolution of 1921, he joined the Mongolian People's Party (MPP) and secured an important position in the Ministry of Finance in 1922. Aligning himself with the leftist faction of the party early on, Sambuu supported the purges and executions of both Dogsomyn Bodoo in 1922 and party leader Soliin Danzan in 1924. In 1926 he was named chief accountant for state receipts and expenditures and called for a tax hike on foreigners (i.e. Chinese merchants) to reduce their control of the economy.