SNP MP Pete Wishart has announced his candidacy to replace John Bercow as the Speaker of the House of Commons.
There is speculation Mr Bercow will announce his retirement this summer, although he has not yet confirmed this.
Conservative MP Sir Edward Leigh and Labour’s Chris Bryant have both voiced an interest in the job.
Mr Wishart wrote on Twitter that he would release a manifesto on Wednesday to become “the first post-war Speaker from beyond the two main parties”.
The Speaker of the House of Commons is in charge of selecting MPs to speak and keeping order during debates. The position is filled via a secret ballot of members.
The position is traditionally seen as an impartial role, and the Speaker is expected to resign from their party.
Mr Bercow has been in the job since June 2009, and was re-elected unopposed after the 2015 and 2017 elections.
There is speculation that he will announce his retirement this summer – although he has not spoken about his plans publicly, always insisting he would tell MPs first.
Labour MP Chris Bryant was one of the first to declare an interest in the job, saying the next Speaker should focus on “tending to the wounds” caused by Brexit rows and harassment scandals.
Sir Edward – who has represented Gainsborough since 1983 – said he would be a “traditional speaker” who did not speak very much.
Mr Wishart – who chairs the Scottish affairs select committee – meanwhile said his candidacy would be “based on a solid agenda of reform seeking to secure equality of all MPs”, saying his manifesto would be “substantial and far-reaching”.
His announcement prompted criticism from some independence supporters online, who told Mr Wishart that SNP members should be at Westminster to “settle up, not settle down”.
But his party leader, Scottish First Minister Nicola Sturgeon, defended the move, saying: “For as long as the SNP is in the House of Commons, we should be trying to make it work as well as we can, and undo some of the barriers that are in the way – we’ve seen all too powerfully in the Brexit debate how Scotland’s voice is not being heard.”
There have also been calls for the next speaker to be a woman, with Labour’s Gloria de Piero and Tory Nicky Morgan saying in a joint article in the Times that electing another man to the post would be a “setback” and a “missed opportunity”.
Dame Eleanor Laing, currently a deputy Speaker under Mr Bercow, has announced her interest in taking up the top job.