He graduated from the nationalist university, Kashi Vidyapeeth, in 1925 and was given the title, 'Shastri', meaning one who is learned in the scriptures. The next year, he joined the `Servants of the People Society' started by Lala Lajpat Rai and plunged into the freedom movement. Shastri married Lalita Devi, the youngest daughter of Ganesh Prasad, in 1928. He did not believe in the dowry system and refused to take dowry. However, on the insistence of his father-in-law he took five yards of khadi cloth as dowry.
Inspired by his political guru, Bapu Purushottamdas Tandon, Shastri joined the Congress Party. He became the City Congress secretary and the president of the Allahabad Congress Committee in 1930. He participated in all national movements between 1921 and 1942 and went to jail seven times. He was elected to the UP Legislative Assembly in 1937.
Once when Shastri was in jail, he received the news that his daughter fell ill. He requested the jailor to release him on parole to attend to his daughter. The jailor granted him 15 days parole. On reaching home, he learnt that his daughter had died. He performed the last rites of his daughter and told his family members that he was going back to the jail. When they reminded him that he was granted 15 days parole, he said, "That was to attend to my sick daughter. But when she is no more, there is no reason for me to take leave."