Former Sikkim CM Pawan Kumar Chamling is the longest-serving Chief Minister with 24 years and 165 days in office. Ex-Odisha CM Naveen Patnaik comes next with 24 years and 99 days in office, followed by Jyoti Basu, who was West Bengal CM for 23 years and 137 days. Ex-Arunachal Pradesh CM Gegong Apang and ex-Mizoram CM Lal Thanhawla come next.