The 67-year-old former journalist was elected as a member for Mid-Scotland and Fife in May 2003.
He said it had been an "immense privilege" to serve his constituents but said he was hoping to return to his former career in broadcasting.Mr Brocklebank was the Scottish Conservatives former rural development and fisheries spokesman but resigned in February 2007 in protest over a policy U-turn.
He was angry that David Cameron stepped back from a threat to withdraw the UK from the EU common fisheries policy.
The Conservative MSP is currently the spokesman for Europe, external affairs and culture.
"It has been an immense privilege to serve the people of Mid-Scotland and Fife and I have greatly enjoyed my time in the Scottish Parliament," he said.Conservative leader Annabel Goldie said the MSP had made "an important contribution" to the Conservative MSP group and to the parliament.
"I don't see myself putting my feet up and playing with the grandchildren. I feel very active.
"I've enjoyed my eight years but I'm equally looking forward to getting back to my old trade."
He added: "It will be good to re-discover my non-partisan voice again, especially on fisheries and media matters."
"His career experience before entering politics has enabled him to be an authoritative commentator on a range of issues but particularly those related to media and culture, " she said.