Six seats vote on Tuesday, from Nandigram to Nagaon, with the count on 9 October

Six by-elections are being held on Tuesday, 6 October, across West Bengal, Tamil Nadu, Assam and Puducherry. The count is due on 9 October. Four are assembly seats: Nandigram and Rejinagar in West Bengal, Madurantakam and Dharapuram in Tamil Nadu. One is an assembly seat in Puducherry, Thattanchavady. One is a Lok Sabha seat, Nagaon in Assam.

Every seat is empty for the same procedural reason. The winner had contested more than one constituency, kept one, and resigned the other. The Representation of the People Act allows a candidate to stand in two places. It requires the extra seat to be vacated within a set period, or both are lost. Tuesday is the bill for that choice, paid by the voter in the seat that was dropped.

Nandigram is the sharpest of the six

Nandigram carries the heaviest recent history of the six. In 2007 police firing on villagers protesting land acquisition for a chemical hub killed 14 people and broke the Left Front's hold on rural West Bengal. Mamata Banerjee later won the seat, lost it in 2021 to Suvendu Adhikari, and the constituency has stayed a personal contest. The BJP has fielded Hasirani Rath, mother of Chandranath Rath, a party aide who was killed. The nomination puts a family of the victim on the ballot in a seat the ruling Trinamool Congress and the BJP have both treated as a symbol. Rejinagar, the other Bengal seat, in Murshidabad, has drawn less national attention and will still produce a full assembly vote in a district the Trinamool and Congress have traded.

In Tamil Nadu the question attached to Madurantakam and Dharapuram is whether defections toward the ruling TVK travel into the booth. A legislator who switches parties can keep a seat until the house acts. A by-election asks the voter to ratify or reject that switch. Dharapuram, in Tiruppur district, and Madurantakam, in Chengalpattu, are the first clean test of that kind since the last assembly election. Thattanchavady, in Puducherry, is a small union-territory seat whose result will move one vote in a 30-member house, which is why it can matter more than its electorate suggests.

Nagaon is the parliamentary one

Nagaon is the only Lok Sabha seat on Tuesday's list. A parliamentary by-election does not change who governs in Delhi. It does change one vote on the floor, and it is the only Assam data point in this round. Assam's state government is BJP-led. A hold or a loss in Nagaon will be read against that, with the limit that one seat is one seat. The vacancy, as with the assembly seats, comes from a double candidacy rather than a death or a disqualification.

Results on 9 October will be the first hard numbers, since the general election, on three arguments at once: whether the BJP can govern and still win a contested by-election, whether opposition parties in these four places can align, and whether Tamil Nadu voters accept the defections that have fed the ruling party. None of the six is a state-wide verdict. Together they are a small, dated sample, with a known cause of vacancy and a known count day.

Polling hours and candidate lists are in the hands of the returning officers. What is already fixed is the map. Two seats in West Bengal, two in Tamil Nadu, one in Puducherry, one parliamentary seat in Assam. Vacant because someone won twice and kept one. Counted on Friday, 9 October.