Sunder Singh Bhandari was also one of his classmates at Kanpur. He started full-time work in the RSS from 1942. He had attended the 40-day summer vacation RSS camp at Nagpur where he underwent training in Sangh Education. After completing second-year training in the RSS Education Wing, Upadhyaya became a lifelong "pracharak" of the RSS. He worked as the "Pracharak" for the Lakhimpur district and, from 1955, as the joint "Prant Pracharak" (regional organiser) for Uttar Pradesh. He was regarded as an ideal swayamsevak of the RSS essentially because ‘his discourse reflected the pure thought-current of the Sangh’. Upadhyaya started the monthly "Rashtra Dharma" publication from Lucknow in the 1940s, using it to spread Hindutva ideology. Later he started the weekly "Panchjanya" and the daily "Swadesh". In 1951, when Syama Prasad Mookerjee founded the BJS, Deendayal was seconded to the party by the RSS, tasked with moulding it into a genuine member of the Sangh Parivar. He was appointed as General Secretary of its Uttar Pradesh branch, and later the all-India General Secretary. For 15 years, he remained the outfit's general secretary. He also contested by-poll for the Lok Sabha seat of Jaunpur from Uttar Pradesh in 1963 bi election when Jansangh MP Bramh Jeet Singh died, but failed to attract significant political traction and did not get elected. In the 1967 general elections, the Jana Sangh got 35 seats and became the 3rd largest party in the Lok Sabha. The Jan Sangh also went onto be a part of the Samyukta Vidhayak Dal, an experiment of having non Congress opposition parties as a coalition to form governments in multiple states This brought the right and the left of the Indian political spectrum on one single platform . He became president of the Jana Sangh in December 1967 in the Calicut session of the party. His presidential speech in that session focused on multiple aspects right from the formation of coalition government to language . No major events happened in the party during his tenure as the president that ended in 2 months in Feb, 1968 due to his untimely death. Upadhyaya edited "Panchjanya" (weekly) and "Swadesh" (daily) from Lucknow. In Hindi, he wrote a drama on Chandragupta Maurya, and later wrote a biography of Shankaracharya.