Independent MSP Dennis Canavan has said that he will not fight the Holyrood election in May.
The MSP for Falkirk West told his constituents his decision in an open letter published on Tuesday.
In it the 64-year-old said that after a great deal of reflection he had decided he would be standing down.
The former Labour MP, whose second son died in December, said he wanted to spend some time with his youngest son, who starts school later in the year.
Mr Canavan was expelled from the Labour Party in 2000 after he stood as an independent at the 1999 Holyrood election when he failed to be selected as an official Labour candidate.
"Over the last few months, I have learned a lot about the value and real priorities of life"
He won the Falkirk West seat in the Scottish Parliament with a majority of 12,192 and was re-elected in 2003 with a majority of 10,000.
The left-winger was first elected as MP for the old West Stirlingshire constituency in 1974 - later becoming Falkirk West MP - and held the seat until 2000.
In 1989, the father-of-five lost his first son Paul to skin cancer.
At the end of December, his 35-year-old son Dennis died of a brain tumour and his eldest son Mark, who lives in Australia, suffers from motor neurone disease.
Thanked constituents
In his letter to constituents, Mr Canavan said: "My youngest son, Adam, who will be starting school this year, is a healthy, happy child and I sometimes wonder what I would do without him.
"I am blessed with a loving daughter and five wonderful grandchildren.
"Over the last few months, I have learned a lot about the value and real priorities of life, and today Adam and I are leaving for Australia for two weeks to spend some time with Mark and his family."
Mr Canavan said it had been a privilege to serve as a politician and he thanked his constituents.
He added that on his return from Australia he would continue to do his best until the dissolution of parliament.
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