The Highlands and Islands MSP, who introduced plans for a smacking ban at Holyrood, will retire at the 2021 Scottish election.
Green MSP John Finnie made the announcement and said he would focus on getting the smacking ban legislation through parliament before he steps down.
A former Highland councillor and ex-police officer, Mr Finnie has also been involved in controversial proposals for a levy on parking at work, which was part of the last Scottish budget.
Mr Finnie’s smacking ban legislation in the form of the Children (Equal Protection from Assault) (Scotland) Bill has been backed in principle by MSPs.
His retirement came as the Scottish Greens began selecting 2021 election candidates.
Mr Finnie, who won his Holyrood list seat in 2011 and was re-elected in 2016, said: “It is an honour to serve the Highlands and Islands in the Scottish Parliament and I intend continuing to work hard until my last day in office.
“I’ve been involved in representative politics since being elected a Highland councillor in 2007 and enjoyed helping people, but I feel the time is right to step aside and let others bring their energy and ideas to what is a demanding job.
“Throughout my time in Parliament, I’ve put my home region of the Highlands and Islands and my constituents at the forefront of my work. Driven by my interest in social and environmental justice, I have been pleased to secure a number of concessions and legislative changes to improve the lives of people in the region.
“At this time, I am focused on working with others to secure the passage of my Member’s Bill giving children equal protection from assault and I hope to see it become law in the near future.
“The climate emergency our planet is facing means that, more than ever, Green policies are required.
“I know there are others who can ensure they are promoted, and delivered, for my home, the Highlands and Islands of Scotland.
“Meanwhile, I look forward to having more time to spend with my family.”