Iain Gray is retiring from the Scottish Parliament at the Holyrood election next May.
The former Labour leader was among the first intake of MSPs when the Scottish Parliament opened in 1999. He's been East Lothian MSP since 2007.
In an email to party members, he said: "The decision to stand down is not an easy one, and was made even harder by the incredibly difficult circumstances we have all faced over the last three months."
Gray, a former teacher, was leader of Scottish Labour at Holyrood from 2008 to 2011.
Gray said: "I will be 64 next year, almost 69 by the end of the next parliament and after more than 20 years at the frontline of Scottish politics, next year is the right time for me to step aside and hand over to someone else to represent East Lothian’s interests.
“I really, genuinely do want to spend more time with my family, especially my wife Gil who has supported me unstintingly through all the ups and downs of political life, and the seven fantastic grandchildren with whom I am now blessed."
Colin Yorkston, chair of East Lothian Labour Party, said: “Local party members will be sad to see him stand down and he will certainly be a very hard act to follow at Holyrood.”
