Rajanna was involved in the cooperative sector since 1972. His public life began around the same period when he served as secretary of the Kyathasandra taluk unit of the Indian National Congress. In 1976, he was elected president of the nagar panchayat Kyathasandra, before heading INC's Youth Congress wing of the Tumkur district-unit between 1980 and 1984.[1]
Rajanna was elected to the Karnataka Legislative Council in 1998 and completed the six-year term till 2004.[1] After being denied an INC ticket to contest the 2004 Legislative Assembly election from Bellavi, Rajanna quit the party and joined the Janata Dal (Secular) (JD(S)),[3] with whose ticket he successfully contested. Rajanna entered the assembly again in 2013, this time from Madhugiri, and again in 2023.[1] He served two terms as president of the Karnataka State Co-operative Apex Bank Ltd., the first from 2001 to 2005, and the second from 2015 to 2020.[4] In May 2023, he was appointed a cabinet minister,[5] and was handed the Cooperation portfolio (excluding Agriculture Marketing).[6]