Kargahar is a key constituency in the Bihar general elections. It is located in Rohtas district of the state. The incumbent MLA on this seat is Santosh Kumar Mishra from Indian National Congress (INC). He won the 2020 Assembly Elections from this seat, securing 59,763 votes. He defeated Bashishth Singh of Janata Dal United (JDU) by a margin of 4,083 votes.

Kargahar has a total registered elector count of 3,29,466 as per 2024 Election Commission data. 1,72,706 of the registered electors from kargahar are male, 1,56,750 voters here are female and 10 electors belong to the third gender. In the 2020 elections the total registered elector count was 3,24,906 where 1,69,621 electors were male, 1,55,273 electors were female and 12 electors were of the third gender. In the 2015 election the total registered elector count in the constituency stood at 2,97,018 where 1,59,207 were male voters, 1,37,800 were female and 11 electors belonged to the third gender. 

In the 2020 elections, 1,94,466 out of the 3,24,906 registered electors cast their votes, which kept voter turnout at 59.85%.  This was similar to the voter turnout in the 2015 elections. That year 1,77,754 out of the 2,97,018 electors took part in polling. 

Polling for this constituency in the upcoming elections will be held in the second phase on November 11, 2025.

This constituency covers an approximate land area of 619.14 square kilometers and the geographic coordinates of Kargahar are 25° 07 '53.4"N 83° 55' 38.6"E. A total of seven Assembly constituencies in the state of Bihar share borders with Kargahar constituency, which are: Rajpur, Dinara, Nokha, Sasaram, Chenari, Mohania and Ramgarh.