Pawan Kumar Chamling is the longest-serving Chief Minister, leading Sikkim for nearly 25 years from December 12, 1994 to May 26, 2019. He is followed by Naveen Patnaik, who first assumed office in 2000 and led Odisha for over two decades. Others in the list include West Bengal's Jyoti Basu, Arunachal Pradesh's Gegong Apang and Mizoram's Lal Thanhawla.