Presiding officer Ken Macintosh won’t seek re-election to the Scottish Parliament in May.
Macintosh, 58, has been an MSP since Holyrood opened in 1999, representing Labour in Eastwood and the West of Scotland.
He suspended his party membership when he was elected to the non–partisan role of presiding officer in 2016.
Macintosh said he was “proud” of the parliament’s achievements over the last two decades, including the introduction of the smoking ban.
In a post on social media, he added: “After much reflection I have decided not to seek re-election to the Scottish Parliament in May next year.
“It has been an honour to represent the people of East Renfrewshire and the West of Scotland for the last two decades and I would thank you for the trust you have placed in me.”