In the following cases, a member of Parliament vacates his seat.
1. Double Membership A person cannot be a member of both Houses of Parliament at the same time. Thus, the Representation of People Act (1951) provides for the following:
(a) If a person is elected to both the Houses of Parliament, he must intimate within 10 days in which House he desires to serve. In default of such intimation, his seat in the Rajya Sabha becomes vacant.
(b) If a sitting member of one House is also elected to the other House, his seat in the first House becomes vacant.
(c) If a person is elected to two seats in a House, he should exercise his option for one. Otherwise, both seats become vacant.
Similarly, a person cannot be a member of both the Parliament and the state legislature at the same time. If a person is so elected, his seat in Parliament becomes vacant if he does not resign his seat in the state legislature within 14 days.
2. Disqualification!I a member of Parliament becomes subject to any of the disqualifications specified in the Constitution, his seat becomes vacant. Here, the list of disqualifications also include the disqualification on the grounds of defection under the provisions of the Tenth Schedule of the Constitution.
3. Resignation A member may resign his seat by writing to the Chairman of Rajya Sabha or Speaker of Lok Sabha, as the case may be. The seat falls vacant when the resignation is accepted. However, the Chairman/Speaker may not accept the resignation if he is satisfied that it is not voluntary or genuine.
4. Absence A House can declare the seat of a member vacant if he is absent from all its meetings for a period of sixty days without its permission. In computing the period of sixty days, no account shall be taken of any period during which the House is prorogued or adjourned for more than four consecutive days.
5. Other cases A member has to vacate his seat in the Parliament:
(a) if his election is declared void by the court;
(b) if he is expelled by the House;
(c) if he is elected to the office of President or Vice-President; and
(d) if he is appointed to the office of governor of a state.
If a disqualified person is elected to the Parliament, the Constitution lays down no procedure to declare the election void. This matter is dealt by the Representation of the People Act (1951), which enables the high court to declare an election void if a disqualified candidate is elected. The aggrieved party can appeal to the Supreme Court against the order of the high court in this regard.