C. Rejith Kumar is actively involved in the Rashtriya Swayam Sevak Sangh (RSS) as a preacher, contributing to the organization's mission and activities. Additionally, he has played significant roles within Thapasya, a cultural and community organization.

From 2016 to 2019, C. Rejith Kumar served as the Thapasya State General Secretary, where he likely played a crucial role in coordinating and overseeing the organization's initiatives during his tenure. Subsequently, he took on the responsibility of Thapasya State Treasurer from 2019 to 2023, managing the organization's financial aspects and ensuring its smooth functioning.

C. Rejith Kumar's dual roles in the Rashtriya Swayam Sevak Sangh and Thapasya demonstrate his commitment to social and cultural causes. As a preacher and organizational leader, he contributes to RSS's ideological and community-building efforts, while his roles in Thapasya highlight his dedication to cultural and community activities at a regional level.