The Chancellor of the Exchequer has appointed Martin McGuinness to be Steward and Bailiff of the Manor of Northstead - the process by which a Member of Parliament resigns their seat.
A by-election will take place at a later date in the constituency of Mid-Ulster.
How an MP vacates their seat
A resolution passed by the House of Commons on 2 March 1624 prohibits MPs directly from resigning their seats.
Death, disqualification and expulsion are the only means by which a Member’s seat may be vacated during the lifetime of a Parliament.
An MP who wishes to resign has to go through the process of applying for a paid office of the Crown, which automatically disqualifies the MP from holding a seat in the House of Commons.
There are two offices which MPs can apply for, Crown Steward and Bailiff of the Chilterns Hundreds and of the Manor of Northstead.
An MP wishing to resign applies to the Chancellor of the Exchequer for one of the offices.
House of Commons Library analysis
The House of Commons Library produces briefing papers to inform MPs and their staff of key issues. The papers contain factual information and a range of opinions on each subject, and aim to be politically impartial.
The Library has published a briefing paper on resignation from the House of Commons which contains more information on the history of the Chiltern Hundreds and Manor of Northstead.
Image: PA/Nick Ansell