At the end of October, Labour MP Barnett announced he would not stand for the Christchurch Central seat again.
Now he has withdrawn entirely, saying he will not put himself forward for the party's list of potential candidates for seats around the country.
"When I announced my departure from Christchurch Central, I left open the possibility of a list nomination. Many have encouraged me to pursue that," he said.
"However, there are exciting horizons for me beyond Parliament and I am keen to explore them."
British-born Barnett, 49, became involved in politics in the United Kingdom before emigrating to New Zealand in the early 1990s.
He was first elected to Christchurch Central in October 1996 and was re-elected three times -- most recently in 2005.
"I have represented Christchurch Central to the best of my ability," he said.
Labour candidate Brendon Burns is set to fight for the seat this year