New members of parliament generally assume office during the parliamentary session following their election. Their mandate is for four years and can be extended if they successfully stand for re-election.
If a member of the National Council steps down during these four years (the legislature period):
if the canton has more than one seat in the National Council, the new member of parliament takes up office at the start of the following session of parliament.
if the canton only has one seat in the National Council, a new election is called in the canton to elect a successor.
Council of States
If a member of the Council of States steps down, a new election is held in the canton to elect a successor.
To officially assume office, members of parliament elected to one of the two chambers of the Swiss parliament must first swear an oath or make a solemn promise. Each member of parliament is free to choose either option. The oath or promise is made on the first day of the parliamentary session following the election – or when a new member replaces an outgoing member of the National Council during the legislature period.
Members of the Council of States re-elected to the same seat are not required to swear an oath or make a promise a second time. However, members of the National Council are required to repeat the oath or promise at the start of each term.
The promise reads: «I solemnly promise to uphold the Constitution and the law and to fulfil the duties of my office to the best of my abilities.»
The oath reads: «I swear by Almighty God to uphold the Constitution and the law and to fulfil the duties of my office to the best of my abilities.»
Anyone who refuses to swear the oath or make the solemn promise declines to take up office.