Sushil Kumar Modi’s  entry into politics began during his student years, where he actively participated in student union activities. This early engagement with political activities shaped his worldview and instilled in him a sense of purpose to serve the people. His association with the Rashtriya Swayamsevak Sangh (RSS) and subsequent joining of the Bharatiya Janata Party (BJP) set the stage for his political journey.

In the initial years of his political career, Sushil Kumar Modi took on various roles within the BJP, from grassroots-level organizing to holding positions of responsibility within the party's organizational structure.

His political was soon recognized, leading to his election to the Bihar Legislative Assembly in 1990. Representing the Patna Central constituency, he embarked on a legislative journey marked by a focus on development, governance, and transparency.

In 2005, Sushil Kumar Modi was appointed as the Deputy Chief Minister of Bihar, serving under the leadership of Nitish Kumar. His tenure as Deputy CM was characterized by collaborative efforts with the Chief Minister to usher in an era of development and progress in Bihar.

In addition to his role as Deputy CM, Sushil Kumar Modi has held several key ministerial portfolios, including Finance, Commercial Taxes, and Forest & Environment. His tenure as Finance Minister was particularly noteworthy. Implementing fiscal policies aimed at boosting revenue generation, promoting investments, and ensuring fiscal discipline, he played a crucial role in strengthening Bihar's economy.